请回答Let him _____to school on a bike 为什么 填go 而不填goes?

Let him __go___to school on a bike 为什么 填go 而不填goes?---这是let 的用法,后面必须接动词原形,--let sb.do sth.
1、He and his father (are playing football )there.就括号内提问 What are he and his father doing?
2、What are these?
They are some apples.请说明原因.
像指示代词做主语的疑问句,回答时必须用适当的人称代词代替：
What's this/that?It's ….
What're these/those?They're ….

Let加动词原形

Let sb. do something
固定搭配