it is the most difficult question to solve为什么solve不用被动态

we found this problem difficult to solve solve为什么不用被动 The problem is easy to solve.为什么用to solve The maths______is difficult to solve. Sometimes it is difficult to solve problems related to g --- We found________ the problem.A it is difficult to solve B it The problem is too difficult for us to solve it. 这个句子里面的it 为 The question is very hard.We can't solve it. It s______ that the problem is difficult to solve.空里填什么? is,so,hard,no way,that,to solve it,the question.we have组成句子 问个英语问题.求教.The problem is much too difficult to solve.为什么不是To this is the problem very difficult to solve the problem is difficult to be solved 为什么solve要是过去式