Here are the correct answers along with brief explanations:

**31. Your school is so green with lots of trees!**
**D. Thank you. We're planting some flowers.**
- Explanation: This response shows appreciation and continues the conversation about the greenery of the school, making it the most natural reply.

**32. If you don't do exercise, you won't be healthy.**
**C. Thank you. I'll exercise more.**
- Explanation: This answer acknowledges the suggestion and implies a willingness to change behavior to prioritize health.

**33. Wow! Your new bike is so cute.**
**C. Yes. My uncle gave me yesterday.**
- Explanation: This response acknowledges the compliment and provides additional information about the bike.

**34. Don't eat much sweet food. It harms your teeth.**
**A. I see. Thank you.**
- Explanation: This answer shows that the person understands the advice and appreciates the concern for their health.

**35. What a lovely hat!**
**B. Thanks. I made it myself.**
- Explanation: This response is an appropriate acknowledgment of the compliment and adds personal pride regarding the hat.

In summary, the correct answers are: 31-D, 32-C, 33-C, 34-A, 35-B.