Those have difficulty in working out the maths problems can ask the maths teathers for advice.这是一道改错题,请问哪里错了?为什么错了呢?

Those have difficulty in working out the maths problems can ask the maths teathers for advice.这是一道改错题,请问哪里错了?为什么错了呢?
Those have difficulty in working out the maths problems can ask the maths teathers for advice.
这是一道改错题,请问哪里错了?为什么错了呢?

Those have difficulty in working out the maths problems can ask the maths teathers for advice.这是一道改错题,请问哪里错了?为什么错了呢?
Those who have difficulty in working out the maths problems can ask the maths teathers for advice
如果不加who
就出现一个主语两个谓语的错误了

those后加who

those 和have 之间加上 Who 定语从句

Those （who）have difficulty in working out the maths problems can ask the maths teathers for advice。
这是定语从句，（who）have difficulty in working out the maths problems修饰those，那些有在数学方面有苦难的人，可以问老师