Here are the best choices to complete each sentence:

21. I like neither this tie **nor** that tie. Could you show me another one?
**Answer:** b. nor

22. **While** I was visiting the Grand Canyon, I bumped into one of my friends from Japan.
**Answer:** a. While

23. **Despite the fact** that he is bright for his age, I think he is a little too young for his class.
**Answer:** a. Despite the fact

24. **Even though** he left earlier than usual, we couldn’t see him off.
**Answer:** a. Even though

25. I'm sure he can remember the details **if** given enough time.
**Answer:** a. if

26. Sound travels at 330 meters per second, **whereas** light travels at 300,000 kilometers per second.
**Answer:** b. whereas

27. **Although** he is quite old, he actively participates in group activities.
**Answer:** a. Although

28. Not only does Steve sing at a bar, **but** he also serves the patrons.
**Answer:** b. but

29. **While** I was waiting in line for a visa interview, I ate my lunch.
**Answer:** b. While

30. He wouldn't say anything **unless** directly asked a question; he was a man of few words.
**Answer:** d. unless

31. **Now that** I'm retired, I can take a long journey throughout Europe.
**Answer:** b. Now that

32. I drive to school **while** my brother always cycles.
**Answer:** d. while

33. I have to go to the meeting **whether** I want to or not.
**Answer:** b. whether

34. You'd better take an umbrella **in case** it begins to rain.
**Answer:** c. in case

35. We're planning to go camping **during** the summer vacation.
**Answer:** a. during

36. **While** I was clean, I took a bath.
**Answer:** b. While

Feel free to ask if you need further explanations or assistance!