to understand the problem is very difficult.(用it作为形式主语）—— ——

to understand the problem is very difficult.(用it作为形式主语）—— —— to understand the problem is very difficult .（改同义句） The problem is very difficult to ( ) I found it is very difficult to understand what the foreigne it's very difficult to understand the english hearing the maths problem is too difficult .——————can work it out The problem is very difficult .You must think it over ------ this is the problem very difficult to solve the problem is very difficult.we can't work it out.(合并）the p The problem is very difficult.He can't work it out.(合并为一句） the problem is very difficult.we can't work it out.(合并一个句）th The problem is very difficult.We can't work it out.(51.合并）