Make a mark--you have any questions. A.in which B.where C.wh

选B.“在你有问题的地方作上标记.”
where you have any questions是状语从句,表示地点.where是从句的中心词.
这个where 前面可以加上in the place .加上in the place 之后,where you have any questions就变成了定语从句,修饰名词place了.这时where就可以换成in which了.
Make a mark in the place where you have any questions.
=Make a mark in the place in which you have any questions.