It has been hypothesized that a chemical known as BW prevents colds. To test this hypothesis, 20,000 volunteers were divided into four groups. Each volunteer took a white pill every morning for one year. The contents of the pill taken by the members of each group are shown in the chart below, Which statement is a valid inference based on the
results?
A. Sugar reduced the number of colds.
B, Sugar increased the number of colds.
C. BW is always effective in the prevention of
colds.
D. BW may not be effective in the prevention of
colds.