Can a vegetarian or low-salt diet reduce blood pressure? Men with high blood pressure are assigned at random to one of four diets:

(1) Normal diet with unrestricted salt;

(2) Vegetarian with unrestricted salt;

(3) Normal with restricted salt; 

(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.