If you could help me out with this MC question, I would appreciate it.

Which of the following would be discharged by commercial impracticability? A contract to buy 5,000 tons of iron for $10 per ton. Two months after the contract is made, the price of iron goes up to $20 per ton, due to an unexpected shortage of railway cars to transport the iron. A contract to sell 5,000 pairs of "Zebra" shoes for $50 per shoe. The shoes are made exclusively in the nation of Fenwick. However, they could be imported from other countries, too. The relations between the U.S. and Fenwick have been deteriorating for years. Each country has threatened the other with war for the last ten years. Shortly after the contract is made, the U.S. declares war on Fenwick and blocks the shoes from importation. A contract to see the New York Mets play the Atlanta Braves on June 28th. The day before the game, three of the starting (C) players were sickened by food poisoning after eating out. The game will be played by three substitute players taking the place of the starting players. (D) None of the above