profit maximization occurs where

a. marginal cost crosses marginal revenue

b. marginal cost crosses average revenue

c. average variable cost crosses average revenue

d. average variable cost crosses marginal revenue

the main difference between the short run and long run isthat:

a. firms earn zero profits in the long run

b. the long run always refers to a time period of one year orlonger

c. in the long run, only one variable can be fixed

d. in the short run, one or more inputs is fixed