逗号when引导什么从句

例句：

When will the single currency be operable?

什么时候实行单一货币？

When's food? I'm starving!

饭什么时候好？我快饿死了！

Some people don't know when they're well off.

有些人身在福中不知福。

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。

When is the best time to ring New York?

什么时间给纽约打电话最好？