A pharmaceutical company tested a new diet drug over a two-month period. The test group of

100 dieters lost an average of five pounds per person during the first month, but gained an average of two pounds per person in the second month. All of the following could help explain the results of the experiment except:

A．The second month of the test occurred during a holiday season, when people are more likely to gain weight.

B．The diet drug has unpleasant side effects, causing many of the subjects to stop using the drug after the first month.

C．The pharmaceutical company provided low-calorie diets to the test subjects in the first month, but let the dieters choose their own food in the second month.

D．The pharmaceutical company selected for the test people who were 20 to 40 pounds over their ideal weights.

E．The diet drug relies on a metabolic effect that loses efficacy the longer a person takes the drug.