Here are the correct answers for the questions provided:

**Question 20:** A. empty (opposite of remote)

**Question 21:** B. take up (opposite of take part in)

**Question 22:** C. mean (opposite of generous)

**Question 23:** D. unfortunate (opposite of fortunate)

**Question 24:** A. way (opposite of solution)

**Question 25:** B. meaningless (opposite of meaningful)

**Question 26:** B. advantaged (opposite of disadvantaged)

**Question 27:** C. was working - met (correct form)

**Question 28:** C. were going - saw (correct form)

**Question 29:** B. were enjoying - were preparing (correct form)

**Question 30:** D. did - was seeing (correct form)

**Question 31:** C. No problem (appropriate response)

**Question 32:** D. donated (correct form)

**Question 33:** C. during (appropriate conjunction)

**Question 34:** A. voluntarily (correct form)

**Combining sentences (using WHEN or WHILE):**

1. I was cycling home last Friday WHEN I saw an old lady on the pavement.

2. Peter was doing the gardening WHEN his mother phoned him.

3. I was walking along the beach WHEN it rained heavily.

4. They were playing online games WHEN their parents came in.

5. While Nam was making a report, Lan was preparing for a cultural exchange event.

6. He was working in a lab WHEN there was a power cut.

Feel free to ask if you need further assistance!