Here are the correct answers for the exercise:

7. **were**
- My parents **were** very pleased because my friends and I volunteered to clean streets 2 days ago.

8. **made**
- I **made** postcards for homeless children last Christmas because I was busy writing a dissertation.

9. **were**
- They **were** happy after the trip to the village near Ha Noi last week.

10. **couldn't**
- Cindy **couldn't** do the homework as she **was** sick yesterday.

**Exercise 6:**
We helped old people at a nursing home **last** Friday.