Which of the Following Choices Correctly Illustrates How Changes in Opportunity

Which of the following choices correctly illustrates how changes in opportunity costs affect supply?

A) A farmer produces corn and wheat. The price of wheat rises; so he shifts his resources towards wheat and the supply of wheat rises.
B) A fisherman fishes for lobsters and oysters. The price of lobsters rises; so he decides to spend more of his time fishing for oysters because he can make the same amount of money with fewer lobsters.
C) A textbook for economics becomes cheaper; so more students opt to buy that particular textbook.
D) Milk and cereal are complementary goods; so when the price of cereal falls, the quantity supplied of milk rises.