The key doesn't fit the lock.
这把钥匙打不开这把锁。
The key has stuck in the lock.
钥匙卡在锁里了。
He could have taken a spare key.
他原本可以带上一把备用钥匙的。
Confidence is the key to success.
信心是成功的关键。
Speed is key at this point.
在这个时候速度是关键。
They zeroed in on the key issues.
他们集中讨论了关键问题。