key以下是什么意思啊

　　例句：

　　Cost was a key element in our decision.

　　价钱是我们决策时考虑的主要因素。

　　Good communication is key to our success.

　　良好的沟通是我们成功的关键。

　　These units played a key functional role in the military operation.

　　这些单位在军事行动中起到了主要的职能作用。

　　The president appears likely to change course on some key issues.

　　总统看起来可能要在某些重要问题上改变方针。

　　I can't think where I put the keys.

　　我想不起把钥匙放哪儿了。