Which Statement Is Not True

Which statement is not true?

A) Herbal remedies and folk medicines abound in most cultures.
B) Most compounds found in plants are likely to have positive physiological effects in humans.
C) A preparation of St.John's wort is believed to be an effective treatment of depression.
D) A major problem with herbal preparations is that no regulatory group controls the purity of the preparations and the concentrations of the active ingredients.