Which of the following statements is true about economies-of-scale experienced in transportation?
a. Transportation cost increases but at a decreasing rate with each additional mile covered.
b. Transportation cost increases but at a decreasing rate with each additional unit added to a shipment.
c. Transportation cost increases but at a decreasing rate with each additional pound (unit of weight) added to a shipment.
d. All of the above
e. Only B and C
