The Figure Shows the Market for Helicopters in the United

The figure shows the market for helicopters in the United States, where D is the domestic demand curve and S is the domestic supply curve. The United States trades helicopters with the rest of the world at a price of $36 million per helicopter.
-In the figure above, the United States ________ helicopters per year.

A) exports 480
B) exports 720
C) imports 480
D) imports 240