Harry Sees an AK-47 Automatic Assault Rifle in a Gun

Harry sees an AK-47 automatic assault rifle in a gun shop window. He inquires about the price and is told that it is $2,500. Harry signs a contract promising to pay the $2,500 on Friday, taking possession of the rifle when payment is made. On Thursday, a law is enacted making the ownership, sale, or possession of an automatic rifle illegal. This contract:

A) automatically terminates due to impossibility.
B) automatically terminates due to impracticability.
C) automatically terminates due to frustration of purpose.
D) is enforceable and not affected by the new law because it was entered into before the law took effect.