Assume that the equilibrium price of French fries rises, while the equilibrium quantity falls. The most consistent explanation for this observation is:

a. An increase in the price of onion rings (a substitute for French fries).

b. A fall in the price of onion rings.

c. A rise in the price of potato bread (production-side substitute for French fries)

d. A fall in the price of potato bread.

Note: the answer is alternative C) and you are asked to argue why it is correct; and further argue why the other alternatives are false or uncertain.