2021 HKDSE 資訊及通訊科技 模擬試題連答案詳解

Which of the following binary numbers represents the value of \(-19_{10}\) in 8-bit two's complement representation?

Which of the following CPU registers is specifically designed to store the memory address of the next instruction to be fetched and executed?

Consider the following pseudocode algorithm segment:

P ← 1
for K from 1 to 4 do
P ← P * 2 + K
output P

What is the output of the algorithm?

A school network assigns IPv4 addresses using a subnet mask of 255.255.255.224. What is the maximum number of usable host IP addresses available in each subnet?

In a spreadsheet application, cell A1 contains the value 8. Cell A2 contains the following formula:

=IF(A1 > 20, "High", IF(A1 >= 10, "Medium", "Low"))

What value will be displayed in cell A2?

Which of the following practices can effectively reduce health hazards associated with prolonged computer use?

(1) Setting the top of the monitor display at or slightly below eye level
(2) Using a wrist rest to maintain a neutral wrist position during typing
(3) Taking short rest breaks periodically

Which of the following statements regarding asymmetric encryption is/are correct?

(1) A public key can be shared openly across the Internet.
(2) A message encrypted with a recipient's public key can only be decrypted with the recipient's private key.
(3) The same secret key is used for both encryption and decryption.

What is the primary benefit of performing disk defragmentation on a traditional magnetic hard disk drive?

Which of the following additions of numbers in 8-bit two's complement representation will result in an overflow error?

During the instruction cycle of a CPU, which of the following registers holds the memory address of the next instruction to be fetched?

What is the output of the following algorithm?

```
val <- 1
s <- 0
for k from 1 to 4 do
val <- val * 2
s <- s + val
output s
```

An online registration form requires users to enter a Hong Kong Identity Card (HKID) number. Which of the following are automated data validation checks that the system can perform directly on the entered data?

(1) Format check
(2) Check digit calculation
(3) Double entry verification

A company network is assigned the subnet address `192.168.50.0/26`. What is the maximum number of usable host IP addresses available in this subnet?

Which of the following measures can help reduce the risk of Repetitive Strain Injury (RSI) for office workers using computer workstations?

(1) Using a wrist rest support when typing and using the mouse
(2) Taking short, regular breaks to stretch and rest muscles
(3) Increasing the refresh rate of the computer monitor

Which of the following tasks are typically executed by client-side scripts rather than server-side scripts on a web page?

(1) Checking if required form fields have been filled before submission
(2) Connecting directly to a backend database to update user account records
(3) Displaying animated image carousels in the user's browser

Given that \(A = \text{TRUE}\), \(B = \text{FALSE}\), and \(C = \text{TRUE}\), which of the following Boolean expressions evaluates to TRUE?

Which of the following 8-bit two's complement binary additions will result in an arithmetic overflow?

In a Central Processing Unit (CPU), which register holds the memory address of the next instruction to be fetched and executed?

What is the final output of the following algorithm?

```text
val ← 27
ans ← 0
While val > 0 do
If (val MOD 2 = 1) then
ans ← ans + 1
val ← val DIV 2
Output ans
```

Which of the following statements regarding IPv4 subnetting is/are correct?

(1) Subnetting isolates network traffic and can reduce unnecessary broadcast traffic.
(2) A subnet with the subnet mask `255.255.255.240` can accommodate at most 14 usable host IP addresses.
(3) Hosts located on different subnets can exchange packets directly without passing through a router or layer-3 device.

A. (1) only
B. (1) and (2) only
C. (2) and (3) only
D. (1), (2) and (3)

Cell `C2` in a spreadsheet contains the formula `=A$1 + $B2`. If cell `C2` is copied and pasted into cell `E5`, what will the formula in `E5` become?

A sound engineer records a 2-minute uncompressed stereo audio track with a sampling rate of \(48\text{ kHz}\) and a bit depth of 16 bits. Which of the following expressions calculates the storage size of the recorded audio file in megabytes (MB), where \(1\text{ MB} = 1024\times 1024\text{ bytes}\)?

Which of the following techniques can help ensure the authenticity and non-repudiation of an email sender?

In relational database design, which of the following statements about foreign keys is/are correct?

(1) A foreign key must reference a primary key or unique candidate key in another table.
(2) A foreign key column can accept `NULL` values unless constrained by `NOT NULL`.
(3) A table can contain more than one foreign key.

A. (1) only
B. (1) and (2) only
C. (2) and (3) only
D. (1), (2) and (3)

Which of the following additions of two 8-bit signed binary integers in two's complement representation will result in an arithmetic overflow error?

Which of the following CPU registers directly stores the memory address of the next machine instruction to be fetched?

An organization is assigned the subnet address \(192.168.50.0/26\). What is the maximum number of usable host IP addresses available within this subnet?

In a spreadsheet, cell `C3` contains the formula `=$A2*B$1`. If cell `C3` is copied and pasted into cell `D5`, what will be the formula in cell `D5`?

Consider the following pseudocode:

```text
A ← [4, 7, 2, 9, 5]
sum ← 0
for i from 1 to 4 do
if A[i] < A[i + 1] then
sum ← sum + A[i]
Output sum
```

What is the output of the algorithm?

Which of the following statements regarding asymmetric encryption (public-key cryptography) is/are correct?

(1) A message encrypted with a user's private key can be decrypted using the corresponding public key.
(2) The sender and receiver must exchange a private key over a secure channel prior to transmission.
(3) A digital signature can verify the authenticity and non-repudiation of the sender.

Which of the following is/are primary functions of an operating system?

(1) Managing CPU scheduling and allocation of main memory
(2) Providing a user interface for interaction with hardware and software
(3) Translating high-level programming language code into machine instructions

A school database includes a table `STUDENT` with the following attributes:

`STUDENT (StudentID, Class, ClassNo, EngName, ChiName)`

Which of the following combinations of attributes can serve as a composite candidate key for this table?

In an 8-bit two's complement representation, what is the result of evaluating the arithmetic expression \(0101\,1010_2 - 0110\,1101_2\)?

During the instruction execution cycle of a central processing unit (CPU), which component is primarily responsible for generating electrical control signals to direct the operation of other units?

An organisation is assigned the network address \(192.168.50.0/26\). What is the maximum number of usable host IP addresses in this subnet?

In a spreadsheet, cell `A1` contains the number `15`, cell `A2` contains `28`, and cell `A3` contains `42`. If the formula `=IF(AVERAGE(A1:A3)>30, SUM(A1:A2), MAX(A2:A3))` is entered into cell `B1`, what is the displayed value?

Consider the following pseudocode algorithm:

```
k ← 1
total ← 0
While k <= 5 Do
If k Mod 2 = 1 Then
total ← total + (k * 2)
Else
total ← total - k
End If
k ← k + 1
End While
Output total
```

What is the output of the algorithm?

Which of the following descriptions about asymmetric encryption is/are correct?

(1) The public key is used to decrypt messages encrypted with the private key.
(2) The sender and recipient share a single identical key for encryption and decryption.
(3) It can be utilised to implement digital signatures for message authentication.

Which of the following measures can effectively reduce the risk of repetitive strain injury (RSI) when working with computers for extended periods?

(1) Using an ergonomic wrist rest while typing.
(2) Adjusting the chair height so that forearms are approximately horizontal.
(3) Increasing the screen resolution to maximum.

When a web form requires a user to input a Hong Kong Identity Card (HKID) number, which of the following validation checks is most suitable for detecting transcription errors in the entered format and check digit?

Mr Lee sets up a smart study lounge at a community centre. The network allows student visitors to access the Internet via Wi-Fi and print revision notes on a shared network printer.

(a) The lounge uses a gateway router connected to a broadband modem, an Ethernet switch, and two wireless Access Points (APs).
(i) State the primary role of an Access Point in this local area network (LAN). (1 mark)
(ii) Give two advantages of deploying two APs instead of a single AP in the study lounge. (2 marks)

(b) Students report that when they move from one corner of the lounge to another, their video streaming disconnects. Suggest a network feature that should be configured across the two APs to allow seamless movement without disconnection. (1 mark)

(c) Mr Lee works on a desktop computer in the lounge for over 7 hours every day.
(i) State one physical health hazard related to the prolonged use of an improper computer display. (1 mark)
(ii) Suggest two ergonomic practices for Mr Lee to alleviate eye strain or neck pain. (2 marks)

(d) The centre provides a web portal for students to book study rooms and make payments.
(i) Explain how HTTPS protects students' credit card information when submitting the booking form. (2 marks)
(ii) Identify the network protocol used to automatically assign IP addresses to students' mobile devices when they connect to the Wi-Fi network. (1 mark)

A school upgrades its multimedia laboratory and considers two computer models, Model X and Model Y, with the following specifications:

$$\begin{array}{|l|l|l|}
\hline
\textbf{Component} & \textbf{Model X} & \textbf{Model Y} \\
\hline
\text{CPU} & 3.6\text{ GHz, 8 cores} & 2.4\text{ GHz, 4 cores} \\
\hline
\text{System RAM} & 32\text{ GB DDR4} & 8\text{ GB DDR4} \\
\hline
\text{Secondary Storage} & 1\text{ TB NVMe SSD} & 1\text{ TB 7200 RPM HDD} \\
\hline
\text{GPU} & \text{Dedicated 8 GB VRAM} & \text{Integrated graphics} \\
\hline
\end{array}$$

(a) Describe what is meant by '3.6 GHz' and '8 cores' in the CPU specification of Model X. (2 marks)

(b) The teacher needs to run 3D animation rendering software in class.
(i) State two reasons why Model X is significantly more suitable than Model Y for 3D animation rendering. (2 marks)
(ii) State one functional difference between System RAM and secondary storage (SSD/HDD). (1 mark)

(c) During video editing, explain how an NVMe SSD improves performance compared to a traditional 7200 RPM HDD. (2 marks)

(d) A student plugs an external drawing tablet into Model X for the first time via USB.
(i) What type of system software must be installed for the operating system to communicate with the drawing tablet? (1 mark)
(ii) If the tablet does not work immediately upon insertion, state two troubleshooting steps the student can perform. (2 marks)

An integer array \( \text{Arr} \) stores \( N \) positive integers, indexed from \( 1 \) to \( N \). A programmer writes the following algorithm to process the elements in \( \text{Arr} \):

```text
K ← Arr[1]
pos ← 1
for i from 2 to N do
if Arr[i] > K then
K ← Arr[i]
pos ← i
temp ← Arr[pos]
Arr[pos] ← Arr[N]
Arr[N] ← temp
```

(a) Suppose \( N = 5 \) and the initial contents of \( \text{Arr} \) are:
$$\begin{array}{|c|c|c|c|c|}
\hline
\text{Arr}[1] & \text{Arr}[2] & \text{Arr}[3] & \text{Arr}[4] & \text{Arr}[5] \\
\hline
14 & 29 & 8 & 35 & 19 \\
\hline
\end{array}$$

(i) What are the values of \( K \) and \( \text{pos} \) after the `for` loop finishes? (2 marks)
(ii) Write down the content of \( \text{Arr} \) after the entire algorithm finishes. (2 marks)

(b) Describe the overall objective accomplished by this algorithm on any array \( \text{Arr} \) of \( N \) positive integers. (1 mark)

(c) The programmer wants to sort the entire array \( \text{Arr} \) in ascending order by repeatedly applying the logic above in an outer loop. Complete the missing parts (1), (2), and (3) of the pseudocode below:

```text
for j from N down to 2 do
pos ← 1
for i from 2 to (1)__________ do
if Arr[i] > Arr[pos] then
pos ← i
temp ← Arr[pos]
Arr[pos] ← (2)__________
(3)__________ ← temp
```
(3 marks)

(d) If \( N = 100 \), how many comparisons between elements (`Arr[i] > Arr[pos]`) will be executed in total during the sorting process? (2 marks)

A fitness club maintains a database table `MEMBER` to store members' workout records. Part of the data is shown below:

$$\begin{array}{|l|l|l|l|c|}
\hline
\textbf{MID} & \textbf{MNAME} & \textbf{GENDER} & \textbf{CATEGORY} & \textbf{HOURS} \\
\hline
M102 & \text{Alice Wong} & \text{F} & \text{Yoga} & 24 \\
\hline
M105 & \text{Brian Chan} & \text{M} & \text{Fitness} & 40 \\
\hline
M108 & \text{Candy Lee} & \text{F} & \text{Yoga} & 18 \\
\hline
M112 & \text{David Cheung} & \text{M} & \text{Swimming} & 32 \\
\hline
M115 & \text{Eva Ho} & \text{F} & \text{Fitness} & 50 \\
\hline
M120 & \text{Frankie Lau} & \text{M} & \text{Fitness} & 30 \\
\hline
\end{array}$$

(a) (i) State the primary key for the table `MEMBER`. (1 mark)
(ii) Suggest one data validation check for the field `GENDER`. (1 mark)

(b) Write an SQL statement to display the name (`MNAME`) and workout hours (`HOURS`) of all female members (`GENDER = 'F'`) who have completed at least 20 workout hours, ordered by `HOURS` in descending order. (3 marks)

(c) What is the output of the following SQL statement?
```sql
SELECT CATEGORY, COUNT(*), AVG(HOURS)
FROM MEMBER
GROUP BY CATEGORY;
```
(3 marks)

(d) The club administrator imports the table into a spreadsheet to calculate reward points. In column F, members who have `HOURS` greater than or equal to 30 receive 2 points per hour; otherwise, they receive 1 point per hour.
Write an Excel formula for cell `F2` using the `IF` function to calculate the reward points for the first record (row 2, where workout hours are in `E2`). (2 marks)

A black-and-white graphic display has a resolution of \( 800 \times 600 \) pixels. Each pixel is stored as a 1-bit binary digit (\( 0 = \text{white} \), \( 1 = \text{black} \)).

(a) (i) Calculate the minimum storage size (in kilobytes, KB) required to store one uncompressed frame of this graphic display. (\( 1\text{ KB} = 1024\text{ bytes} \)) Show your calculation. (2 marks)
(ii) If the display is updated to support 256 distinct colours, what is the new minimum number of bits required to represent each pixel? (1 mark)

(b) The system uses a simple Run-Length Encoding (RLE) scheme to compress rows of pixel data. Each run of consecutive identical pixels is represented by a pair: `(Colour, Count)`, where `Colour` is `W` for white and `B` for black, and `Count` is a positive integer.

For example, a row of 10 pixels `W W W B B B B W W W` is encoded as:
`W3 B4 W3`

(i) Encode the following row of 16 pixels using this RLE scheme: (2 marks)
`B B B B B W W W W B B B B B B B`

(ii) Decode the following encoded stream into the original sequence of pixels: (1 mark)
`W4 B2 W6 B3`

(iii) State one scenario where RLE will result in an encoded file size that is larger than the original uncompressed file. (1 mark)

(c) The school creates a digital comic book containing these graphics and publishes it on the school website.
(i) State one intellectual property right that protects the original comic artwork. (1 mark)
(ii) Explain why adding a digital watermark or Creative Commons licence can help the creator manage their intellectual property. (2 marks)