That, Who, Which

That, who and which introduce more information about a person, thing or idea.

The woman that lives next door is very friendly.
Could I speak to the nurse that I saw yesterday, please?
The dog that won the contest is standing over there.

The person who told me had seen it herself.

It was the green car that caused the accident

 

That is usual in spoken English. In written English use who with people and which with things.