A promise by Derkin Restaurants to buy all of the produce it needs this next year at an established price from Elfredo's Produce would be an:

a) unenforceable promise based on past consideration.

b) enforceable output contract.

c) enforceable requirements contract.

d) unenforceable, illusory contract.

C) enforceable requirements contract.

Explanation:

A requirements contract is a contract between one organization and its vendor. The vendor agrees to supply as much of a good or service that the organization may need and require, and the organization agrees to only purchase the good or service from that specific vendor.

In this case, Elfredo agrees to supply all the goods needed by Derkin, and Derkin agrees to buy the goods it needs only from Elfredo.