Question

why is a placebo used in double-blind drug test? choose one option a to prevent people from having side effects from the drug b to keep the cost of the experiment down c so that everybody in the experiment thinks they took the medicine, but nobody did d so that the subjects and the scientists do not know which group is the control group

Explanation:

• Option A: Placebos don't prevent drug side effects; they are inert, so A is wrong.
• Option B: Placebos aren't used to reduce cost; their role is experimental control, so B is wrong.
• Option C: In a double - blind drug test, the experimental group takes the real drug and the control group takes the placebo. Not "nobody did", so C is wrong.
• Option D: In a double - blind study, both subjects and researchers are unaware of who is in the control (placebo - taking) or experimental (drug - taking) group. This reduces bias, which is the purpose of using a placebo in such a test.

Answer:

D. so that the subjects and the scientists do not know which group is the control group