1.关系代词指代先行词在定语从句中作表语时只用that，但时常省略。
She is no longer the girl that she used to be. 她不再是过去那个女孩儿了。
2.以the way为先行词的限制性定语从句，通常以in which或 that 引导，但通常省略in which或 that。
The way (in which) he spoke to his classmates was unfriendly. 他跟同学说话的方式并不友好。
3.以reason为先行词的限制性定语从句，如果先行词reason在定语从句中做状语，通常以why引导，但人们通常省略why。
That is the real reason (why) they left their hometown. 那是他们离开家乡的真正原因。
4.在there be 句型中，关系代词总是被省略。
There is a lady (who) wants to talk with you. 有一位女士想和你谈谈。
还有其他情况的省略，需要大家平时点滴积累。
