that, who, which

that, who, which

He told me that his house was new (object)
The man that lives near the post office is my brother-in-law (relative pronoun)

relative pronouns

who → people
which → objects, places, ...
that → can substitute who or which but only when they are not between the two commas (= only when they are defining)



She is the girl who was taken to the hospital.
That girl, who is my sister, goes to school where your dad teaches.
The girl who(m) you met at the cinema is from Canada.
Feltre, which is close to the mountains, is in the north-east of Italy.
The town which I told you about is Feltre.
The street which is now closed to the traffic is an ancient Roman road.


Therefore, only in some sentences you can do that change:

She is the girl that was taken to the hospital.
That girl, who is my sister, goes to school where your dad teaches.
The girl that you met at the cinema is from Canada.
Feltre, which is close to the mountains, is in the north-east of Italy.
The town that I told you about is Feltre.
The street that is now closed to the traffic is an ancient Roman road.


Moreover, you can decide not to use the pronoun if the subject of the relative clause is not the relative pronoun:

She is the girl who was taken to the hospital. (who is necessary because it is the subject of   the relative clause)
That girl, who is my sister, goes to school where your dad teaches.
The girl you met at the cinema is from Canada. (here the subject is you, so you don't need the pronoun)
Feltre, which is close to the mountains, is in the north-east of Italy.
The town  I told you about is Feltre. (here the subject is I, so you don't need the pronoun)
The street which is now closed to the traffic is an ancient Roman road. (which is necessary because it is the subject of the relative clause)