Final answer:
Anker is relying on the defense of force majeure to excuse their inability to deliver the necessary coal under the contract.
Step-by-step explanation:
Anker is relying on the defense of force majeure to excuse their inability to deliver the necessary coal under the contract. Force majeure refers to unforeseen circumstances that prevent a party from fulfilling its contractual obligations. In this case, Anker claims that physical difficulties at the mine and a change in regulations hampered their ability to extract coal. These circumstances are beyond Anker's control and would qualify as force majeure events.