The pronoun can be omited?
The book which I bought yesterday is great.
The book I bought yesterday is great.
The woman ___ is singing is my teacher.
The woman that is singing is my teacher.
The woman is my teacher. She's wearing a red dress.
The woman who is wearing a red dress is my teacher.
The girl who called you is my friend.
CAN'T be omited because "who" is the subject.
The book ____ I borrowed was very interesting.
The book I borrowed was very insteresting.
The movie which we watched last night was exciting.
The movie we watched last night was exciting.
I don't know the reason ____ he left early.
I don't know the reason he left early.
She visited the town. The town was founded in 1800.
She visited the town which was founded in 1800.
The man who lives next door is very kind.
CAN'T be omited.
This is the house ____ my parents lived when they were young.
This is the house where my parents lived when they were young.
I met a man. His son is a famous musician.
I met a man whose son is a famous musician.
The house that Jack built, which is now abandoned, is very old.
THAT can be omited, but WHICH no because is the subject of the sentence.
The man ____ car was stolen reported it to the police.
The man whose car was stolen reported it to the police.
The scientist made a groundbreaking discovery. She received an international award for it.
The scientist, who made a groundbreaking discovery, received an internacional award for it.