1. Why did Sam go to the dentist's? (have a toothache)

   Because he has a toothache.

2.  Why didn't you take part in volunteer programs? ( not have enough time)

   Because I didn't have enough time.

3. Why doesn't Mike want to go and see the film? (see it already)

   Because he sees it already.

4. Why does Sharon popular in school? (be honest and polite)

   Because Sharon is honest and polite.

5. Why did the teacher scold Alex? (not complete his homework)

   Because she didn't complete his homework.

6. Why did you go late last night? (miss the last bus)

   Because I missed the last bus.

Giải thích:

Why + trợ động từ + chủ ngữ + động từ?

Because + mệnh đề.