题目内容：

随机应变：根据括号中所给的单词，填入正确的单词形式。将答案写在答题卷的相应位置上。

1. He left the room without ________________ (say) a word.

2. He volunteers ____________ (offer) to clean up the city park.

3.The higher the ground is, the______________(thin) the air will become

4.I want him to know the idea of ________ (fair).

5.I was__________(sweep) the floor at 8:00 yesterday morning.