All we can do is look at mug shots.这句话的句子成分怎么分析?

题目

All we can do is look at mug shots.这句话的句子成分怎么分析?
all we can do 是个什么成分?是主语从句?那连接词呢,到哪里去了?这个结构是特殊的结构吗?

答案

All (that )we can do 是主语从句,that 可省略.all that =what 可以改写 what we can do ,可以作为一个固定的表达记住它!
All sb can do is ...
For example:All I can do is wait
All she can do is stay at home watching tv.