Question

为什么 To do today's homework without the teacher's help is very difficult.的主语中心词为to do?

Answer 1

To do today's homework without the teacher's help是本句主语，without the teacher's help是修饰，所以To do today's homework是主语中心词。

without the teacher’s help是个介词短语，可以作定语也可以作状语，如果作定语，介词短语应该修饰它前面的名词。如果作状语，就应该修饰它前面的动词，故这个介词短语应该是作状语。

to do作主语

例句：

It is not easy to find your way around the town.

正这个小镇找到路很不容易。

由于主语太长了，放到了后面，前面用虚主语it代词，构成形式主语。

作表语

例句：

Anyhow, my goal is to provide humans with a life of high quality.

总之，我的目标就是为人类提供高质量的生活。

Answer 2

To do today's homework without the teacher's help是本句主语,without the teacher's help是修饰,所以To do today's homework是主语中心词.