Assume that labor is the only factor of production and that wages in the United States equal $20 per hour while wages in Japan are $10 per hour. Production costs would be lower in the United States as compared to Japan if
选项：

A: U.S. labor productivity equaled 40 units per hour and Japan's 15 units per hour.
B: U.S. labor productivity equaled 30 units per hour and Japan's 20 units per hour.
C: U.S. labor productivity equaled 20 units per hour and Japan's 30 units per hour.
D: U.S. labor productivity equaled 15 units per hour and Japan's 25 units per hour.
E: U.S. labor productivity equaled 15 units per hour and Japan's 40 units per hour.