Relative clauses

What relative pronouns to use?
I told you about the woman ___ lives next door.
Do you see the cat _____ is lying on the roof?
He couldn’t read _____ surprised me.
Do you know the boy _____ mother is a nurse?
I was invited by the professor ____ I met at the conference.
This is the shop _____ I bought my bike.
The reason ____ we met him is unknown.

Defining relative clauses (no comma)
The writer who/that wrote The Grapes of Wrath is my favourite author.
In the letters which/that she never opened everything was explained.
The boy (who/whom/that) we met yesterday is very nice.

Non-Defining Relative Clauses (with comma);
NO „that“!
John Steinbeck, who wrote The Grapes of Wrath, is my favourite author.
In the letters, which she never opened, everything was explained.
Jim, who/whom we met yesterday, is very nice.

Relative pronouns – necessary or not?
(We can leave object pronouns in defining clauses only)
The book which I bought is not very good.
The Thames is a river which runs through London.
A guide is a person who shows tourists around a place.
Cheese is food which mice like eating.
https://www.ego4u.com/en/cram-up/grammar/relative-clauses/exercises?10

Common mistakes
SOMETHING, ANYTHING, NOTHING….never use „what“!
He said something that / which I liked.
(NEVER USE: He said something what I like)
The boy which did it will be punished.
He did nothing what I liked.
Where is the girl, who sells the tickets?
The stone fell on my head was quite big.
It is the song, that I like a lot.
This is the only way how to learn English