Is this museum the one they visited last month? 这个博物馆是他们上个月参观过的那个博物馆吗？

A. that    B. the one    C. which    D. the one who

如果网友把这个句子变为肯定陈述句再分析。就知道为什么要选B答案，而不选C答案。

This museum is the one (that/which 可省略) they visited last month.

这家博物馆就是他们上个月参观过的的博物馆。

This museum【主语】// is【系动词】// the one 【表语】//(that/which 可省略) they visited last month【修饰表语后置定语】.

备注(1):that/which they visited last month为定语从句修饰先行词the one，关系代词that/which代替先行词the one并在定语从句作谓语动词visited的宾语。

备注(2)：one为替代词用法，替代museum.如果选择B答案which会出现2个错误。错误(1)逻辑错误，This museum is  which they visited last month.(错误英语句子)。错误(2) 定语从句没有先行词。

【1】This museum is the one (that/which 可省略) they visited last month.【正确】

【2】This museum is which they visited last month.【错误】

特别备注：which引导表语从句，主句的主语必须是“表示疑问的名词”

The question is which is better.问题是哪一个更好。

备注：which引导表语从句并在表语从句作主语。

The question is which they want.问题是他们想要哪一个。

备注：which引导表语从句并在表语从句作谓语动词want的宾语。