Explain the following in one or two paragraphs:
a. why in the long-run perfect competition, price is at a minimum average cost.
b. why marginal revenue is less than price in monopoly.
c. what is price discrimination and what are the conditions for it to occur and why
d. why is it that when technology is taken into account, we cannot be sure what market structure (perfect competition or monopoly) will be the lowest cost?