The math problem seems very easy but in fact it is very difficult.A. to work outB. being

问题补充：

The math problem seems very easy, but in fact it is very difficult.

A. to work out

B. being worked out

C. working out

D. to be worked out.

答案：

(答案→)A. to work out

B. being worked out

C. working out

D. to be worked out.

解析：考查非谓语动词。句型S（人，物）+ be + adj. + to do，句子的主语在逻辑关系上为不定式动作的宾语，to do中的动词是及物动词时，不用被动，不及物动词后要接介词。句意：这道数学题看起来非常容易，但事实上却很难解出来。故A正确。