2. The letter mailed last night will reach him tomorrow.

1. The man sitting on the platform is a professor from Wuhan University.

4. You are welcome to a party to be given in our class at 7:45.

说明：以上的定语从句部分可以用更加简单的非谓语形式表达出来：

3. The question that is being discussed is very important.

2. The letter that was mailed last night will reach him tomorrow.

1. The man who is sitting on the platform is a professor from Wuhan University.

4. No one believes the reason that he gave us about his absence at the meeting.

(三)定语从句的简化表达：

3. I think I can understand the reason why he didn’t tell the truth to me.

2. This is my hometown which I used to talk about to you.

1. I’m very glad to return to my hometown where I had lived for 10 years.