Which of the Following Was NOT a Reason Why OPEC

Which of the following was NOT a reason why OPEC failed to keep the price of oil high?

A) over the long run, producers of oil outside of OPEC responded to high prices by increasing oil exploration and by building new extraction capacity
B) consumers responded to higher prices with greater conservation
C) consumers replaced old inefficient cars with newer efficient ones
D) the agreement OPEC members signed allowed each country to produce as much oil as each wanted