可以组成单词when，意思是……时候，例如：

1.When will the single currency be operable 什么时候实行单一货币？

2.When's foodI'm starving!饭什么时候好？我快饿死了！

3.Some people don't know when they're well off.有些人身在福中不知福。

4.I didn't use to like him much when we were at school.以前我们同学时，我并不太喜欢他。