Twelve People,who Suffer from Chronic Fatigue Syndrome,volunteer to Take Part

Twelve people,who suffer from chronic fatigue syndrome,volunteer to take part in an experiment to see if shark fin extract will increase one's energy level.Eight of the volunteers are men and four are women.Half of the volunteers are to be given shark fin extract twice a day and the other half a placebo twice a day.We wish to make sure that four men and two women are assigned to each of the treatments,so we decide to use a block design with the men forming one block and the women the other.Suppose one of the researchers is responsible for measuring if a subject displays an increase in energy level.What design principle should be added to this experiment?

A) Use two placebos.
B) Use a stratified sampling design to assign subjects to treatments.
C) Use fewer subjects but observe them more frequently.
D) Conduct the study as a double-blind experiment.