This isdifficult problem that few students can work it out.A. soB. so aC. suchD. such a

问题补充：

This isdifficult problem that few students can work it out.

A. so

B. so a

C. such

D. such a

答案：

A. so

B. so a

C. such

(答案→)D. such a

解析：so、such 区别So，如此，那么，用法是so+形容词，such,如此，那么。用法是：such+(a/an)+(形容词)+名词，但名词前有few,little,many,much修饰时只用so. 组成句型，so…that…或so …that…,句意：这个问题如此的难，以至几乎没有同学能算出。故选D。