could后面加什么介词

could,情态动词后要跟动词原型,而“介宾”结构是不能直接放在情态动词后的,所以要组成系表结构，而系动词的动词原型是be.所以could 后面要用be；

could

modal 用于can的过去时;(询问是否可做某事)能，可以;(礼貌地请求别人做事)能；

v. 把(食品)装罐保存;让…卷铺盖走人;炒…的鱿鱼

This could cause serious damage to the country\'s economy.

这可能对国家的经济造成严重破坏。

The database could be used as a teaching resource in colleges.

数据库可以用作大学里的.一种教学辅助手段。

I think we could all use a drink after that!

我想我们在事情办完之后都得痛快地喝一杯。

He could just make out three people through the mist.

透过薄雾他勉强能看出有三个人。

The operation could prolong his life by two or three years.

这次手术可使他多活两三年。

only with a few people could she be her real self.

只有和几个人在一起时，她才能表现出真实的自我。