The problem is very difficult to ( )

The problem is very difficult to ( )

这个问题主要是work out这个词组本身具有主动意义，记住这点就行了。英语中并不是说事情或某工作某问题总是被人去做，看一下下面这这些例句就知道了。

work out
解决, 解答; 计算出
This problem will not work out.
这个问题解答不了。
She worked out the problem with no difficulty.
她毫无困难地解决了这个问题。
The area can easily be worked out if you know the length and the breadth.
如果你知道长度与宽度, 面积很容易计算出来。
The charge for labor works out at almost ten shillings an hour.
付给工人的费用算下来每小时差不多十先令。
I can't work out how to do it.
我无法解答怎么做它。
Can you work out on the map where we are now?
你能在地图上找到我们现在所在的位置吗?
产生结果; 发展
The plan worked out badly.
计划进行不顺利。
Everything has worked out according to plan.
一切都按计划发展。
锻炼
These athletes work out at the gym for two hours every day.
这些运动员每天都要在体育馆锻炼两个小时。
作出; 制订出
It wasn't too long before we had worked out a plan acceptable to all.
没多久我们就制订出一个大家都能接受的计划。
The plan has already been worked out, and could be put into operation at a moment's notice.
计划已经拟好并立即可以付诸实施。
使筋疲力尽; 耗尽
He never seems to be worked out.
他好像永远不知疲乏似的。
了解某人的本质
You're cunning, and I can't work you out.
你这个人太狡猾, 我实在看不透你。
在外当雇工
Jimmy worked out when he was only ten.
吉米在十岁时就离家去当雇工了。

相当于It's difficult to work out the problem.(只助于理解）．to work out表目的

因为在这里不用被动，而且已经有了BE动词。

已经有BE动词了，不能再用be