这题答案选d，怎莫感觉c好像也对阿？

harvard2012

A nutritionist studying the effects of massive doses of vitamin C found that of a group of 600 people who regularly took 1,500 mg of vitamin C daily for a year, fewer than 9 percent suffered serious cases of flu; of a group of 600 people who took 250 mg of vitamin C (the standard recommended daily allowance) daily for a year, 34 percent suffered at least one serious case of flu; and of a group of 600 people who took no vitamin C for a year (other than that found in the foods in a balanced diet), 32 percent suffered at least one serious case of flu.
Which of the following hypotheses is best supported by the evidence above?
(A) The effectiveness of vitamin C in preventing serious cases of flu increases in direct proportion to the amount of vitamin C taken.
(B) Vitamin C is helpful in preventing disease.
(C) Doses of vitamin C that exceed the standard recommended daily allowance by 500 percent will reduce the incidence of serious cases of flu by 25 percent.
(D) Massive doses of vitamin C can help to prevent serious case of flu.
(E) A balanced diet contains less than 250 mg of vitamin C.