Is ____ easy _____ out the maths problem?

问题描述:

Is ____ easy _____ out the maths problem?
Yes.You can work it out in three minutes.
A.this;to work b.this;working C.it;working D.it;to work
说明原因

D
it是形式宾语,指代work out the maths exam
后者要跟to do sth