The problem was too diffcuclt for __ to solve.We had to ask

The problem was too diffcuclt for __ to solve.We had to ask It is easy __ the problem.A,for him solve B,for him to solve The problem is too difficult for us to solve.=The problem___ 写出同义句 the problem is too difficult for ue to solve. The math problem is too diffcult for me to solve后为什么不能加it The problem is too difficult for us to solve it. 这个句子里面的it 为 we had to___ to solve the maths problem A .tried our best B. we had to___ to solve the maths problem A.tried our best B.t help to solve the problem? He found that the problem was hard to solve. to solve the problem ,we need more r___ 问个英语问题.求教.The problem is much too difficult to solve.为什么不是To