be used to doingUSED是什么词?

be used to

习以为常.

通常不分开看,

就像be able to =can一样,你可以当成形容词吧.强调一种状态.used习以为常的状态.

It's supposed to be an adjective.
As you see, "used" is a word after "be".
Consequently, In this sentence "used" is an attribute.

这整个是一个固定句型，习惯于做某事。
当成形容词用吧

你只要知道啥意思就行啊 ，习惯做某事，used不用变。