The Assumption That a Firm Operates in a Competitive Labor

The assumption that a firm operates in a competitive labor market means that

A) the firm offers a real wage rate that is indexed for inflation.
B) the firm faces an upward-sloped marginal cost of labor curve.
C) the firm faces a downward-sloped marginal cost of labor curve.
D) the firm faces a constant wage regardless of how much labor it employs.
E) the firm doesn't use capital in the production process.