A homeowner hires a contractor to build a deck made out of knotty pine timbers. In fact, using knotty pine timbers is the contractor's specialty. After the contract is executed, but before performance a massive wildfire destroys much of the knotty pine forest, significantly reducing the availability of wood. The knotty pine becomes so scarce that in order to build the deck, the cost would be three times more than the original price. A court determines that under these circumstances, the contractor's obligation has been discharged.

Which type of discharge is this?

A. Impracticability

B. Frustration of purpose

C. Material breach

D. Impossibility