The teacher asked such a difficult question ___ no one in the class could answer.
A.which B.that C.so D.as
答案：D
这是个含有定语从句的主从复合句,先行词（a difficult question）被such或者the same修饰时,关系代词用as,并且关系代词在定语从句中作answer的宾语.
翻译：老师问了一个班上没有人可以回答的很难的问题.
解惑：如果从句中answer有宾语,那它就不是定语从句了,而是结果或程度状语从句了,即：The teacher asked such a difficult question _B_ no one in the class could answer（it）.A.which B.that C.so D.as
答案：B
翻译：老师问了个如此难的问题,以至于班上没有人可以回答它.