A state law declares a wild pig to be an endangered species and prohibits the killing or shooting of any wild pig within the state. A new national park was established by the federal government to preserve plants and animals native to the region, and is located entirely within the state. The wild pig is so hardy that it has begun to displace other wildlife in the national park. Because the wild pig is actually descended from European stock, the United States Department of the Interior has contracted with an exterminator, a resident of another state, to kill all wild pigs living within the national park. The contract with the exterminator is specifically authorized by federal statutes regulating the operation of nationalparks.

If the exterminator is prosecuted by the state for violating the law that prohibits the killing of wild pigs, which of the following is the exterminator's strongest argument in defense against that prosecution?

(A) Only the federal government can declare a species to be endangered.

(B) As applied, the state statute unduly interferes with interstate commerce.

(C) As applied, the state statute violates the Obligation of Contracts Clause of the United States Constitution.

(D) As applied, the state statute violates the Supremacy Clause of the United States Constitution.