求道代词指代的问题

ljwqlcl881703

In assessing the problems faced by rural migrant workers, the question of whether they are better off materially than the urban working poor is irrelevant.
(A) In assessing the problems faced by rural migrant workers, the question of whether they are better off materially than the urban working poor is irrelevant.
(B) The question of whether the rural migrant worker is better off materially than the urban working poor is irrelevant in assessing the problems that they face.
(C) A question that is irrelevant in assessing the problems that rural migrant workers face is whether they are better off materially than the urban working poor.
(D) In an assessment of the problems faced by rural migrant workers, the question of whether they are better off materially than the urban working poor is irrelevant.
(E) The question of whether the rural migrant worker is better off materially than the urban working poor is irrelevant in an assessment of the problems that they face.
BE 最后that they face 中答案给的解释是they没有指代对象 意思是对前面the rural migrant works 和 the urban working 指代不明 还是就是不能指代这俩中的一个
如果有资料求一份GMAT代词指代的讲解链接~~ 万分感谢