To See If Eating Just Before Going to Bed Causes

Multiple Choice

To see if eating just before going to bed causes nightmares, volunteers are recruited to spend the night in a sleep laboratory while connected to machines that monitor their sleep patterns. They are randomly assigned to be given a meal before bed or not. Numbers of nightmares are recorded and compared for the two groups. The critics claim the study

A) gives results that do not generalize.
B) does not use a placebo.
C) is not precise.
D) cannot establish causation because it is an observational study.