선생님들!! 질문있습니다!! 급해요!!ㅜㅜㅜ(관계대명사 계속적용법)

I bought a book, which I found it boring

He gave me the letter, which was in a blue envelope.

The house, which has a big tree, was built in 2010.

she is studying math, which many people hate.

She secretly loves her neighbor, who is an ordinary banker.