Explanation:

- Simplex (Option 1):

- Data flows in one direction only.

- Example: Keyboard to Monitor, as it only sends data one way without feedback.

- Correct Answer: Simplex

- Half Duplex (Option 2):

- Data flows in both directions, but not simultaneously.

- Think of a walkie-talkie: speaking and listening happen one at a time.

- Full Duplex (Option 3):

- Data flows in both directions simultaneously.

- Similar to a phone call, allowing ongoing two-way communication.

- Option 4 (a and b):

- Implies both simplex and half duplex, which isn’t applicable here.