Mehran has heard from some of his team-mates that drinking a high protein supplement after football training will improve his muscle mass. He decides to test this hypothesis by examining the effect of a high protein drink on some of his team-mates compared with what happens with a control group who drink only water. Which of the following would be the best control for his experiment?
a) randomly selected team-mates who are given only small amounts of a protein drink.
b) randomly selected team-mates who are given a placebo instead of a protein drink.
c) volunteers from the general campus population who are not given any protein drink.
d) volunteers from the general campus population who begin football training and are given a protein drink.
e) volunteers from the football team who agree to take a placebo instead of a protein drink.