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 percent on the average.
B) There was only a minor effect on reducing the number and severity of colds.
C) There was a slight, but consistent, reduction in the duration of colds in people who consumed at least 200 g a day.
D) There was a significant reduction in the number of colds only in people who consumed more than 3 g per day.