The key doesn't fit the lock.

　　這把鑰匙打不開這把鎖。

　　The key has stuck in the lock.

　　鑰匙卡在鎖里了。

　　He could have taken a spare key.

　　他原本可以帶上一把備用鑰匙的。

　　Confidence is the key to success.

　　信心是成功的關鍵。

　　Speed is key at this point.

　　在這個時候速度是關鍵。

　　They zeroed in on the key issues.

　　他們集中討論了關鍵問題。