The director of a community recreation center conducted a six-week study to examine the effects of four types of exercise—strength training, flexibility training, aerobics, and jogging—on maximal oxygen consumption. From the 40 members who participated, the director randomly assigned 10 members to each exercise type. Maximal oxygen consumption was measured for each member at the beginning of the study and again at the end of the six weeks. The director examined the change in maximal oxygen consumption for each member. Which of the following statements is a correct description of a feature of the study?
a. The study has replication because there are four types of exercise.
b. The study has replication because it was conducted over a six-week period.
c. The response variable is the type of exercise with the greatest change in maximal oxygen consumption.
d. The treatments in the study are strength training, flexibility training, aerobics, and jogging.
e. The experimental units are the four different types of exercise.