A Study Attempts to Determine Whether a New Medication Is

A study attempts to determine whether a new medication is effective at lowering blood pressure. Forty subjects with hypertension who volunteer to participate in the study are to be given both the new medication and a placebo. The order in which each subject receives the treatment is randomized, and the subjects do not know which treatment they are getting. Each treatment is administered for four weeks. At the end of each four-week period a subject's blood pressure is recorded.
What are the experimental units in this study?

A) The medication taken by the 40 subjects who volunteered.
B) The 40 subjects who volunteered
C) The subjects who experienced a reduction of blood pressure
D) The subjects who didn't experience a significant reduction in blood pressure.