题目内容：

I can think of many cases ____students obviously know a lot of English words and expressions but can't write a good essary.
A why B which C as D where
为何答案为D

优质解答

where指的是many cases中的的意思.
以下供参考：
That is just where you are wrong.
那正是你错误所在.
where it's (all) at
重大事件发生的地点; 问题的核心所在
where sb.is at
某人的处境; 某人的实际情况