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

A.that      B.which       C.while      D.as

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

1. A.
   that
2. B.
   which
3. C.
   while
4. D.
   as

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

A. that    B. which     C. while    D. as