All you have to do is..结构的问题

All you have to do is stand still and look stupid.

如此的结构中,为何is可以直接和动词原形的stand / look放在一块,中间无需to隔开或者用动名词形式?

*这里的still讲解为何?

All you have to do（主语）is （系动词）stand still and look stupid.

如此的结构中,为何is可以直接和动词原形的stand / look放在一块,中间无需to隔开或者用动名词形式?

*这里的still讲解为何?

【答】All you have to do 是主语，is 是系动词，stand still and look stupid 是由 and 连接的两个动词不定式短语充当表语。

假如主语部分有行为动词do 的某种形式（谓语动词或非谓语动词均可），充当表语的动词不定式可以带或者不带to。所以：

All you have to do is stand still and look stupid.

=All you have to do is to stand still and look stupid.