안녕하세요. 가정법 문제를 풀다가 의문이 생겨서 질문해요.

if he _______ to the teacher attentively, he ________ the
answer to the problem.
① had listened ; would know
② listened ; would know
③ listened ; would have known
④ had listened ; would have known

이 문제의 답은 4번인데, 저는 2번도 된다고 생각해요.
if s 과거동사, would/could/should 동사원형 용법을 이용하면요 그래서
2번도 여기서 답이 될지 궁금하네요. 질문 하나 더할께요.
전치사+whic』?which,(whome)용법을 잘모르겠네요.
어떤 문장에서는 목적격 역할을 또는소유격역할을 하기도하고 언제 어떻게사용할지 개념이 적립이 안잡히네요. 도움 구합니다^^ 아래는 예문이요.
the picture (for which)he paid 2,000 dollars was drawn by a famous painter.
spouse means a person(to whom) the person is married.
the building (of which)windows are bright at night is our school library.