Bessemer Inc., a producer of steel, has plants fueled by coal. For several years, it has placed individual orders for coal each month with Coal Mining Company (CMC). On January 1 of this year, Bessemer and CMC signed a written contract obligating Bessemer to purchase "its entire requirements of coal" for the next three years from CMC. Bessemer is to notify CMC on the 15th of each month how much coal it requires for the next month. The contract is:

A. Unenforceable because Bessemer's promise is illusory (it has not committed to purchasing any specific amount of coal) B. Enforceable, subject to a duty of good faith, as a requirements contract C. Unenforceable, because it is too indefinite D. Enforceable, subject to a duty of good faith, as an output contract