Cheever
                    College offers several online courses via remote computer connections, in addition to traditional classroom-based courses, a study of student performance at Cheever found that, overall, the average student grade for online courses matched that for classroom-based courses.  In this calculation of the average grade course withdrawals were weighted as equivalent to a course failure, and the rate of withdrawal was much lower for students enrolled in classroom-based courses than for students enrolled in online courses.

A Among students who did not withdraw, students enrolled in online courses got higher grades, on average, than students enrolled in classroom-based courses.

B The number of students enrolled per course at the start of the school term is much higher, on average, for the online course that for the classroom-base courses.

C There are no students who take both anonling and a classroom-based course in the same school term.

D Among Cheever College students with the best grades, a significant majority take online, rather that classroom-based, courses

E Courses offered online tend to deal with subject matter that is less challenging than that of classroom-based courses.

题干说online courses 学生的grade 和classroom-based courses的一样,但前者退出率高过后者，就可以推出前者没退出的学生的平均grade高过后者吗？（A项答案解释）

那怎么知道退出的是成绩好的还是坏的？还是我的中文翻译理解错了？   求大家帮看看

withdrawals were weighted as equivalent to a course failure，哦，那就是说退出等同于失败，就是说，凡是退出，就是O分了。这样就会拖累平均分了。原来是我理解成：退出还是有成绩的。

谢谢提醒！