A Researcher Is Interested in the Effects of a Vegetarian

A researcher is interested in the effects of a vegetarian diet on memory. One group eats a strict vegetarian diet for three months, a second group eats a strict vegan diet for three months, while a third group eats anything they want for three months. After three
Months, all participants are given a memory test. The first 20 people who participated
Were assigned to the vegetarian group, the next 20 to the vegan group, and the final 20 to the eat anything group. What's wrong with this experiment?

A) It is confounded because of a possible experimenter bias effect.
B) It is confounded because there was no random assignment.
C) The experimenter introduced some demand characteristics.
D) There is nothing wrong with this experiment.
E) It is confounded because the study cannot be replicated.