帮忙解释下这个定语从句题吧

Human facial expression differ from those of animals in the degree____ they can be controlled on purpose.

A with which B to which C of which D for which

tell me why,please! Thank you ~

选B to which

1.Human facial expressions differ from those of animals in the degree。人的面部表情在一定程度上说是有别于动物的面部表情的。those 在这里代替facial expression
2.to which they can be controlled on purpose.这句话是定语从句！主语they谓语can be controlled 介词on purpose。可见：从句中并不缺主语，to which 应该是做状语！所以，which 应该代替degree,degree 应该是先行词！翻译：出于这个原因（程度）人的面部表情（they)可以有目的的被控制！

就是选B哦。 to which 是因为 degree 的缘故。 degree to which 在定语从句中是固定搭配，就像 key to 那种一样。

C of which

in the degree of something 固定搭配