A production possibilities curve that is linear (a straight line):

a. illustrates a tradeoff in which opportunity cost of a good increases with the level of its production.
b. illustrates a tradeoff in which the opportunity cost of a good decreases with the level of its production.
c. illustrates a tradeoff in which the opportunity cost of a good is constant at all levels of production.
d. demonstrates the fallacy of composition.

c