Research Question: What is the combined effect of coffee and how it was prepared on blood pressure?
A randomized, controlled experiment investigated this question using a random sample of 540 adult males as subjects. At the beginning of the study, researchers measured the blood pressure of all the subjects. Each subject was given a regular or decaffeinated coffee, which was prepared by either boiling (Turkish coffee), filtering (drip brewing), pressure (espresso), or steeping (French press). At the end of the month, the researchers measured the blood pressure of each subject again, and compared the two blood pressure readings.
How many different groups are there altogether in this study?
A 2
B 4
C 6
D 8
E 16