Which of the Following Represents the Results of Well-Controlled Studies

Which of the following represents the results of well-controlled studies of vitamin C supplementation on the resistance to,and recovery from,colds?

A) There was a reduction in the duration of colds by 50% on the average
B) There was only a minor effect on reducing the number and severity of colds
C) There was a consistent reduction in the duration of colds in people who consumed at least 200 mg a day
D) There was a significant reduction in the number of colds only in people who consumed more than three grams per day