A Researcher Claims That the Mean Resting Pulse Rate of All

Multiple Choice

A researcher claims that the mean resting pulse rate of all college basketball players in the United States is less than the mean resting pulse rate of all professional basketball players in the United States. The resting pulse rates of a random sample of 115 college basketball players were measured as were the resting pulse rates of a random sample of 80 professional basketball players. The mean resting pulse rates of the two groups were compared.
In this study, the explanatory variable is

A) the level of basketball played (college or professional) .
B) the number of players studied in each group.
C) the resting pulse rate.
D) confounded with the placebo effect.