题目内容：

请根据所给的中文补全下列各句，每条横线上只能填写一个单词。

1.他经常遭受各种病痛的煎熬。

He often             different illnesses.

2.这本书非常有趣，很值得再读一次。

The book is so interesting that it is            for a second time.

3.他们听到这个笑话时都忍不住大笑起来。

They             laughing when they heard the funny joke.

4.我们应保护环境，以免它受到破坏。

We should       our environment       being destroyed.

5.他总是很乐意帮助别人，从来没有想到过得到回报。

He is always ready to help others and never expects anything   ____