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。