mary is often early for school.为什么用for 不用to

Question

如题所述

Answer 1

因为没有动词的情况下直接说to school是不合语法的，只能理解成school是一个地点，必须说go to school之类，那这个句子应该是Mary is often go to school early.
而for可以直接跟名字，school就可以理解成“上学”而不是“学校”。

Answer 2

mary is often early for school = mary is often early to go to school

Answer 3

be for 吗？