I know the girl. The girl works in IBM.
I know the girl who / that works in IBM.
The old man is a famous artist. We visited the old man yesterday.
The old man who /that we visited yesterday is a famous artist.
The laptop is made by DELL. I bought the laptop last week.
The laptop which / that I bought last week is made by DELL.
He is the hardest-working student that I have ever taught.
He is the first man that finished the work on time.
3.先行词被only, just, the same, next等词修饰：
This is the only dictionary that I have at hand.
Is there anything that I can do for you?
We know nothing about the doctors and the hospitals that you are talking about.
We have to protect whales and sharks that are being threatened by death.