Answer:
C.
Explanation:
The only way to minimize this effect would be through randomization of students in morning and afternoon classes. Doing so apply the factor of skill from an individual student to either time of day class greatly lessens the overall effect that it has on the results. This therefore, minimizes the effect it has on the experiment itself, since the same students that have been studying in a certain time of day would be randomized and not have the same environment that they are used to.