中等ECON-PRDC-017
The law of diminishing marginal returns starts to apply when:
A. All inputs are varied together in the long run.
B. Adding more of a variable input, with at least one input fixed, eventually lowers marginal product.✓ 答案
C. Total product becomes zero.
D. The firm becomes a monopoly.
解說
Diminishing marginal returns is a short-run idea: some input is fixed. After a point, extra units of the variable input add less and less output. It is not a statement about market structure, and total product can still rise while marginal product falls.