A Double- Blind Placebo- Controlled Study Is

A double- blind placebo- controlled study is

A) research that involves looking at factors in two or more groups of subjects to see if there is a relationship to certain outcomes.
B) research in which neither the subjects nor the scientists know which group received the treatment and which group received a placebo.
C) an idea generated by scientists based on their observations.
D) a stepwise process used by scientists to identify effective placebos.