It is hard for students to get good grades in school. But the hardest

It is hard for students to get good grades in school. But the hardest problem met by students' parents is that the students do not want to get good grades, and even an eight-year-old child could take example of "successful without good grades" people such as Steve Jobs and Bill Gates to explain his bad grades. To improve students' academic performance, education professor Roland Fryer decides to let students get paid on the basis of metrics such as attendance, behavior, tests and class work.

Which of the following, if true, most seriously weaken the Roland Fryer's conclusion above?

(A) Students will be more interested to be paid on attendance and behavior than to be paid on tests and class work.
(B) Incentivizing students with money can make students give up their free time and invest more time to school work.
(C) Students who get paid from their parents may spend the payment on smoking and drinking.
(D) Not all parents want their children to get good grades in school tests.
(E) Money is not always the best incentive for students to have good grades in school.