Students shouldn’t be given so difficult a problem they can not work out.A. thatB. whichC.

问题补充：

Students shouldn’t be given so difficult a problem they can not work out.

A. that

B. which

C. while

D. as

答案：

A. that

B. which

C. while

D. as

解析：在定语从句中，当先行词被so/such修饰时用as引导定语从句。