Earth Movers & Shakers operates 3 iron ore mines. The table below shows each mine’s total daily production and the current number of miners at each mine. All miners work for the same wage, and each miner in any given mine produces the same number of tons per day as every other miner in that mine. The opportunity cost of moving one miner from Mother Lode to another mine is:
A.1 ton per day.
B.3 tons per day.
C.2 tons per day.
D.4 tons per day.
正确答案：4 tons per day.
