求助一个WEAKEN题

Of the students graduating from Governor Smith Academy, a private high school, 93% go on to college. From Eastern High, the public high school in the same city, only 74% go on to attend college. As a result, many parents with children about to enter high school believe that Governor Smith Academy gives students a better education than the can get at Eastern High School.

Which of the following statements, if true, would cast the most doubt on the conclusion about Governor Smith Academy?

a.       Until 1922, Governor Smith Academy was exclusively a girls’ school, but Eastern High School has always been coeducational.

b.       Governor Smith Academy requires students to pass an admissions examination before entering, but Eastern High School admits all applicants who live in the city.

c.       Eastern High School has problems with severe student violence during school hours.

d.       Governor Smith Academy has a higher percentage of students attending Ivy League colleges than any other high school in the state.

e.       Eastern High School receives its funding from local property taxes, while Governor Smith Academy receives funding from tuition costs and from alumni donations.

对这道题比较迷惑，感觉似乎没有正确答案，a，e是无关选项，b，c，d是加强结论，尤其是b，既然有一个入学考试，更说明对学生要求严格。书上正确答案是b，请各位指教。

原文argument:家长认为入学率高是因为Governor Smith Academy有更好的education.

B则认为是因为前者学生的生源比后者好，导致前者入大学的比率多。

他因导致，所以weaken。

其他几个选项都似乎无关。