prep sc 17 求助

17。Rejecting the apprenticeship model of training social workers in philanthropic agencies, twentieth-century reformer Edith Abbott was convinced of social work education belonging in the university so that students could be offered a broad range of courses dealing with social issues.

(A) of social work education belonging in the university so that

(B) that social work education should be in the university, and that

(C) about the importance of social work education belonging in the university while

(D) that social work education belonged in the university, where

(E) of the necessity of social work education being in the university and

答案是(D)，请问为什么belonged 要用ed 形式？

多谢大家帮忙。

因为convinced that后面的动词要和主句动词的过去式保持一致，所以要用过去时

我比较纠结的是B选项，觉得意思上面也是可以的，只不过多了一个should情态动词，请问nn这个是不是错误点，如果不是的话B选项错在何处？