A randomized experiment was done by randomly assigning each participant either to walk for half an hour three times a week or to sit quietly reading a book for half an hour three times a week. At the end of a year the change in participants' blood pressure over the year was measured, and the change was compared for the two groups.

The two treatments in this study were:

a. Having blood pressure measured at the beginning of the study and having blood pressure measured at the end of the study.
b. Walking or reading a book for half an hour three times a week and doing nothing.
c. Walking or reading a book for half an hour three times a week and having blood pressure measured.
d. Having blood pressure measured at the beginning of the study and walking or reading
e. Walking for half an hour three times a week and reading a book for half an hour three times a week.