A study of a new medication found that patients who took the medicine have reduced blood pressure, compared to those who did not take the medicine. The research team concluded that the medicine caused the reduction in blood pressure. Which study design did they most likely use? (2 points)

a
They most likely used an experiment with patients randomly assigned to take the medicine or not take the medicine.

b
They most likely used an experiment with patients randomly assigned to groups based on their blood pressure.

c
They most likely used a survey asking patients if they took the medicine and how their blood pressure was affected.

d
They most likely used a survey asking patients if they took the medicine and if they felt the medication helped their blood pressure.