A Health Psychologist Is Interested in the Effectiveness of a New

A health psychologist is interested in the effectiveness of a new exercise on reducing the rate of heart attacks because the exercise requires no equipment and, therefore, can be done without cost.
-What is the null hypothesis?

A) People will not participate because it does not cost them any money.
B) The exercise will make no difference in the rate of heart attacks.
C) The exercise will make no difference or will reduce the rate of heart attacks.
D) The exercise will make no difference or will increase the rate of heart attacks.