The quantity of labor that a profit maximizing firm will employ, holding other input factors constant, is the level at which:（）
A. the marginal revenue product of labor is equal to the wage rate.
B. the marginal product of labor is equal to the marginal cost of labor.
C. one more unit of labor would cost less than the value of its additional output.
参考答案：A
解析：
For any productive input, including labor, a profit maximizing firm will employ additional units of the input until its marginal revenue product is equal to its price (the wage rate is the price of labor). If one more unit of labor would cost less than the value of its additional output, the firm will increase profits by adding that unit. A firm’s labor demand curve is the entire range of output over which it realizes diminishing marginal returns from labor input. Marginal product is measured in units of output and cannot be compared directly to marginal cost, which is measured in units of money.