逗號when引導什麼從句

例句：

When will the single currency be operable?

什麼時候實行單一貨幣？

When's food? I'm starving!

飯什麼時候好？我快餓死了！

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.

以前我們同學時，我並不太喜歡他。

When is the best time to ring New York?

什麼時間給紐約打電話最好？