there are three rooms in the new flat,_____ serves as my study

题目

there are three rooms in the new flat,_____ serves as my study
A the largest one
B the largest room
C the largest of them
D the largest of which
为什么选D?AB为什么不可以?
怎么看出来是定语从句的？

答案

which是指the new flat,D意为新公寓里3个房间中比较大的是我的书房~the new flat后面是一个逗号,下半句没有连接词所以选D,如果the new flat后面是and没有逗号,就选AB~