例句：
When will the single currency be operable?
什么時候實行單一貨幣？
When's food? I'm starving!
飯什么時候好？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，我并不太喜歡他。
When is the best time to ring New York?
什么時間給紐約打電話最好？