If we want to give extra information about a noun, and an adjective (Lesson 64) is not enough, we can use a relative clause. Relative clauses often begin with one of the relative pronouns: who, which, that, where and whose.
I know a man who played hockey for the Edmonton Oilers.
He played hockey.
Do you know the woman that can help us?
She can help us.
I want a word which means 'very surprised'.
It means 'very surprised'.
The two cars that caused the accident drove away.
They caused the accident.
Britain is one country where they drive on the left side of the road.
They drive on the left side of the road there.
Do you know the man whose daughter is a doctor?
His daughter is a doctor.
if it is an OBJECT PRONOUN (Lesson 50)
The doctor - I go to studied in Canada. (I go to him.)
The students - I know are very friendly. (I know them.)
if the first verb in the relative clause is be.
Did you see the man - standing by the door? (who was standing)
The boy - knocked down by the car was John. (who was knocked)