If labor is the only variable input and it costs $15 per hour and if the marginal product of labor is 3 units per hour, the short-run marginal cost of 1 unit of output is approximately $0.20 Answer A: $0.20 A $3.00 Answer B: $3.00 B $5.00 Answer C: $5.00 C $15.00 Answer D: $15.00 D $45.00