求助这道6选2

Psychologists have discovered that some of the most _______ advice on study habits is flat wrong, leading them to revise the guidelines they offer to students.
A. popular B.hallowed C. respected D. unassailable. E. effective F. beneficial

答案CD跟BC我都见过，我个人感觉BD也可以，主要是BCD这三个词太接近了不知道怎么选才合适。 求大佬解答