Which of the following is (are) true statement(s)?

a. Prices provide incentives for buyers and sellers.

b. Higher prices for a good or service provide incentives for buyers to purchase less of that good or service and for producers to make or sell more of it.

c. Lower prices for a good or service provide incentives for buyers to purchase more of that good or service and for producers to make or sell less of it.

d. All of these statements are correct.