钥匙的复数

　　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。