A Wide Variety of Substances, Such as Rhinoceros Horn, Are

A wide variety of substances, such as rhinoceros horn, are believed to be aphrodisiacs. A good way to determine whether rhinoceros horn does indeed increase sexual performance would be to

A) give experimental subjects powdered rhinoceros horn and then measure sexual function.
B) give subjects a placebo but tell them they are getting rhinoceros horn, and then measure sexual function.
C) give subjects either rhinoceros horn or a placebo and then measure sexual function.
D) give experimental subjects powdered rhinoceros horn and then measure testosterone levels.
E) study the sexual behavior of rhinoceroses in the wild.