问题补充：
The math problem was difficult none of us worked it out.
A. very; that
B. too; to
C. so; that
D. enough; that
答案：
A. very; that
B. too; to
(答案→)C. so; that
D. enough; that
解析：句意：这道数学题太难了以至于我们中谁也做不出来。so...that...如此……以至于……；too...to...太……而不能,to后接动词。故选C.
