1 B. where; that
句子强调的是 It was in the theatre that the murder took place. 谋杀就发生在这家剧院里.
__where___the Phantom of the Opera was put on是 theater 的定语从句
这家剧院曾经上演歌剧.
2 D.to whom
句子的主句部分为：the number of people is very large.人数很多
sth happened to sb 是某是发生在某人身上 的意思
3 D.for whom
have respect for
尊敬[重], 重视
上面三个题目都是讲的关于 定语从句的
要注意一些短语 以及介词的固定搭配