分类：教育/科学-外语学习
问题：Whenyoureadthebook,youhadbetterm? 
When you read the book ,you had better ma a mark _________ you have any question .A.at which B.at where C.where (为什么不选A.B?) 
回答：反正是固定用法
mark后面就要接where
如同case situation后面也只能接where