Suppose you are investigating how the diet of hamsters affects how much they run on their hamster wheel. in order to control the experiment, which of these should you do?
a.
change only the diet of each hamster.
b.
give all the hamsters the exact same diet.
c.
only allow some hamsters to run on the wheel.
d.
compare the behavior of hamsters and gerbils.

A. Change only the diet of each hamster.

Explanation:

If you want to know the relationship between the hamsters' feed and the way they run in the wheel of their cages, you should give each hamster a different feed and evaluate the way they behave in the wheel, the speed they run, the time that run, among other factors.

You must offer a different food for each hamster to be able to compare the results, if you give the same food to all hamsters the results can be the same, so you will not be able to compare which food showed the best results and which showed the worst results.