Can changing diet reduce high blood pressure? Vegetarian diets and low-salt diets are both promising.

Men with high blood pressure are assigned at random to four diets: (1) normal diet with unrestricted salt; (2) vegetarian with unrestricted salt; (3) normal with restricted salt; and (4) vegetarian with restricted salt. This experiment has

(a) one factor, the type of diet.

(b) two factors, high blood pressure and type of diet.

(c) two factors, normal/vegetarian diet and unrestricted/restricted salt.

(d) three factors, men, high blood pressure, and type of diet.

(e) four factors, the four diets being compared.