有几个问题我实在没搞懂,请高手指教。

wushuang313

原文段落：（og12 RC 44题  page377)
（15)A complicating factor has been the continuing
        lack of specialized one-volume reference works on
       Asian Americans, such as biographical dictionaries
       or desktop encyclopedias. Such works would
       enable students taking Asian American studies
（20)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, given such works, Asian
（25 American studies professors might feel more free to
        include more challenging Asian American material in
        their introductory reading lists, since good reference
        works allow students to acquire on their own the
        background information necessary to interpret
（30 difficult or unfamiliar material.

问题 ：The passage suggests that the factor mentioned in lines 15–18 complicates professors’ attempts to construct introductory reading lists for courses in Asian American studies in which of the following ways?

答案：By making it more necessary for professors to select readings for their courses that are not too challenging for students unfamiliar with Asian American history and culture。

注解：If students had good reference works to consult for background information necessary to interpret  difficult or unfamiliar material, then their professors might feel more free to include more challenging Asian American material in their
introductory reading lists. This sentence suggests that professors currently do not include challenging material on their reading lists because  it is too difficult or unfamiliar for their students.
有几个问题我实在没搞懂,请高手指教。
第一：注解前半段是我看完文章对问题的理解，标黄的部分实在搞不明白.
第二：25行 用的“might” 是过去式，但是27行出现 since. 有since出现不是应该用完成时态吗？？ 谢谢！

edison890424

回答一下你的第二个问题。If the students had... the professors might... 是比较明显的虚拟语气，和过去式没有什么关系。since 在文中的意思是因为，并不引导完成时态。

由于不知道你对前半句以及全文的理解究竟是什么，没有办法回答你的第一个问题。