The product process matrix or graph (PPM) was developed by Robert H. Hayes and Steven C. Wheelwright. Few years later, Roger Schmenner developed the Service Process Matrix (SPM). Select the best answer choice. There is only one correct answer. Group of answer choices

a. In SPM, the production volume (ranging from low to high volume) is represented in the X-axis, and the degree of product customization (ranging from low to high customization) is represented in the y-axis.

b. In SPM, the degree of product customization (ranging from low to high customization) is represented in the X-axis, and the product volume (ranging from low to high volume) is represented in the y-axis.

c. In PPM, production volume (ranging from low to high volume) is represented in the x-axis and the degree of product customization (ranging from low to high customization) is represented in the y-axis.

d. In PPM, the degree of interaction with customers and customization of service (ranging from low to high interaction/customization) is represented in the X-axis, and the degree of labor intensity is represented in the y-axis.

e. a and d are true.