请问下that在各种从句中的省略问题！（什么从句能省？什么情况下能省？）

一.在引导宾语从句时一般可以省除以下几种情况.
1.宾语从句为虚拟语气时.如He suggested that we should take more exercise.
2.宾语从句为两个,前一个引导词可以省略.后面的不能.
3,宾语从句中还有其它从句时不能省略.如 His father promised that if he passed the exam ,he would buy him a bike.
二.在定语从句时先行词作宾语时可以省略关系代词that
The book (that)I bought yesterday is very interesting.

简单回答：在宾语从句中可以省；在定语从句中做宾语的时候可以省