20.When you read the book,you’ d better make a mark _____ yo

20.When you read the book,you' d better make a mark _____ you have any questions.
A.at which B.at where C.the place D.where

You'd better make a mark where you have any questions.
You`d better make a mark at the place where you have any questions.
以上两句字意思相同,但第一个是状语从句,后一个是定语从句.定语从句不管是where还是which要有先行词THE PLACE,而状语从句没有.状语从句中where引导的句子做地点状语,不出现place.
定语从句出现先行词place,再用where引导的定语来修饰place
所以选D