1. 同义句转换，每空一词。

1. （1） Planting trees every year is necessary for us.

   for us to plant trees every year.

3. （2） I spend half an hour doing morning exercises every day.

   It me half an hour to morning exercises every day.

5. （3） They kept on talking until the teacher came in.

   They didn't until the teacher came in.

7. （4） The teacher said, "Don't cheat in exams, children."

   The teacher asked the children cheat in exams.

9. （5） I think that it is important to learn English well.

   I think to learn English well.