It was for this reason her parents moved out of London and settled down in a mountain vil

问题补充：

It was for this reason her parents moved out of London and settled down in a mountain village.

A. that

B. which

C. why

D. how

答案：

(答案→)A. that

B. which

C. why

D. how

解析：如果选择why构成定语从句，则需要去掉this reason前的for，所以这里不是定语从句。因为去掉it was和that，剩下的是一个完整的句子，所以是强调句型，强调句的结构It is/was+被强调部分+that+句子的其他成分