The maths problem was too difficult for students of our grade ___

问题描述:

The maths problem was too difficult for students of our grade ___
A.to answer B.to answer it C.to work out D.to work it out
Many people think___necessary to have a good knowledge of an second when looking for a good job.
A.that B.it C.which D.if

C..
It's +adj.for sb.to do sth.
work out the maths problem
B..
sb.think it +adj.to do sth.