在剧院 前面的冠词到底用in还是at

1.at the theater 听戏剧。in the theater.在戏院。例句They are at the theater.他们在听戏剧。We are in the theater.我们在戏院。

2.He is a doctor.He works in the hospital.

3.Let's go to school.My English teacher works in a school.He gets there by bike.