An Instructor Wishes to Find Out Whether a New Teaching

An instructor wishes to find out whether a new teaching method is superior to his usual procedures,so he conducts an experiment.Everyone in his classes is quite excited about the prospect of learning under the new procedure but of course he cannot administer the new teaching method to everyone.A random half of the students receive the new method and the remaining half receive the old.What is the most obvious flaw in this experiment?

A) Subjects should have been systematically assigned to groups.
B) The sample is not representative of the population.
C) Placebo effects or experimenter bias are likely to affect results.
D) Distortions in self-report will affect results.