I'll give you a key so that you can let yourself in.
我把鑰匙給你，你可以自己開門進去。
The key is hanging on a string by the door.
鑰匙拴在門邊的`帶子上。
The need to communicate is a key characteristic of human society.
需要交流是人類社會最重要的一個特徵。
Cost was a key element in our decision.
價錢是我們決策時考慮的主要因素。
Good communication is key to our success.
良好的溝通是我們成功的關鍵。