relative clauses

[daisy1352]

Please reduce these relative clauses:
The boy who is painting is my little brother.
I'd like to read the book which is on the table.

Where do you use which:
The letters came today. They are late.

[Casiopea]

The boy who is painting is my little brother.
The boy painting is my little brother.

I'd like to read the book which is on the table.
I'd like to read the book on the table.


The letters came today. They are late.
The letters which came today are late.