[求助]一道笔试题难以区分选项!

这是杨继书里一篇说亚裔美国人研究缺乏单卷本参考书的文章,相信大家都有印象吧,有一个问题我弄不明白,抄在下面,大牛们多多帮咱看看,指点一下迷津:

文章说(第一段省掉)
A complicating factor has been the continuing lack of specialized one-volume reference works on Asian Americans, such as biographical dictionaries or desktop encyclopedies. Such works would enable students taking Asian American studies courses (and professors in related fields) to look up basic information on Asian American individuals, institutions, history and culture without having to wade through mountains of primary source material. In addition, give such works, Asian American studies professors might feel more free to include more challening Asian American material on their introductory reading lists, since good reference works allow students to aquire on their own the background information necessary to interpret difficult or unfamilliar material.
Q: the passage suggests that the factor mentioned in the first line complicates professors'attempts to construct introductory reading lists for courses in Asian American studies in which of the following ways?
混淆答案

D) such courses were offered only at schools whose liberaries were rich in primary sources
(E) By making it more necessary for professors to select readings for their course that are not too challenging for students unfamiliar with Asian American history and culture.
the right answer is D but mine is E.?[em07]