Consider the following statements: I. The standard cost per unit of materials is used to calculate a materials price variance. II. The standard cost per unit of materials is used to calculate a materials quantity variance. III. The standard cost per unit of materials cannot be determined until the end of the period. Which of the above statements is (are) true? Select one: a. I, II, and III. b. II only. c. I only. d. I and II. e. III only.