A computer is so useful a machine we can use everywhere.A. thatB. whichC. asD. what

问题补充：

A computer is so useful a machine we can use everywhere.

A. that

B. which

C. as

D. what

答案：

A. that

B. which

(答案→)C. as

D. what

解析：本题考查句子结构和关系代词的选用。首先表示认清句子结构，use后面应该接一个及物动词，先行词应该充当宾语，而前面出现so useful不能用that与which来修饰，可以排除。另外，what 不能引导定语从句。