Here are the best answers to complete each space:

21. a. amusing
22. d. drove
23. b. in
24. a. Not
25. b. slow

So, the completed sentences would be:

I had an **amusing** experience last year. When I **drove** to town in the south of France, a young man waved to me. I stopped and he asked me for a lift. As soon as he had got into the car, I said good morning to him **in** French and he replied in the same language. **Not** of us spoke during the journey. I myself know a little of French. I had nearly approached the town when the young man suddenly said, very **slow**, "Do you speak English?" As I soon learnt, he was English himself.