SAT语法一道--为什么指代不明?

题目

SAT语法一道--为什么指代不明?
OG08-S10-12
Many changes occurred while she was president of the (college, and they increased its educational quality as well as effectiveness).
(A)college, and they increased its educational quality as well as effectiveness
(B)college, they both increased the educational quality and effectiveness of the college
(C)college, which both increased its educational quality as well as increased its effectiveness
(D)college; these changes increased its educational quality and effectiveness
(E)college; these changes increased both the educational quality and effectiveness of the college
其中我对AD两个选项有疑问.官方解释是这样的:Choice (A) involves a lack of parallelism and the use of vague pronouns. The two objects of the verb "increased" are not grammatically alike: the pronoun "its" is needed to precede the second object, "effectiveness," as it precedes the first, "educational quality."
Choice (D) involves the use of a vague pronoun. The meaning of the sentence would be clearer if the pronoun "its" were replaced by a possessive noun, "the college's."
1. 不知道AD怎么vague了
2. A中increased its educational quality as well as effectiveness非要加its才平行吗?
谢谢

答案

AD都没有明确指出it代指的是college,虽然也不能算错,太多介词让句子不太清晰加个college更好,所以有college的选项就选better的