Allegheny Energy Supply Co. and Monogahela Power Co., a subsidiary, filed suit against Anker West Virginia Mining Co., later acquired by International Coal Group, for breach of contract. The parties had a contract for Allegheny and Monogahela to buy all of the coal produced from a proposed "Sycamore 2" mine, located in Harrison County, W.Va. The coal promised amounted to about 1.8 million tons per year, not less than 20 million tons total. Anker has never produced the necessary amount of coal, topping out at 480,000 tons per year in total from the mine. Anker had sent a letter to Allegheny in 2006 claiming physical difficulties at the mine and a change in the enforcement of regulations relating to coal mining near gas wells hampered their ability to extract coal from the mine. As a result, Anker said it was unable to deliver the necessary coal. Which defense to performance is Anker relying on?
A) Misrepresentation
B) Parol evidence
C) Failure of conditions
D) Force majeure

Based on the information provided within the question it can be said that in this scenario Anker is relying on Force Majeure as a defense to performance. This term refers to any kind of unforeseeable circumstance that may prevent an individual or company currently in a contract from fulfilling a their obligations that they have agreed to in the contract. Such as what Anker is stating happened to them.