题目内容：

用所给动词的适当形式填空

1.Too much homework _________ (lead) to students’ poor health.

2.Work harder, and you             (get) better grades in your lessons.

3.John’s mother often hears him ____________（sing）in his room, and the songs are beautiful.

4. — Look! The little boy is swimming in the river.— I ________ (not know) he could swim.

5.Someone _____________ (knock) at the door, go and see who it is.

6.We should prevent people from               wild animals. (kill)

7.They did everything they could___________the animals in danger. (protect)

8.You will fail in the exam if you          (not be) careful.