key以下是什麼意思啊

例句：

The key has stuck in the lock.

鑰匙卡在鎖裏了。

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。