The Market Demand Curve for Labor

The market demand curve for labor

A) is determined by adding up the quantity of labor demanded by each firm at each wage, holding constant the other variables that affect the willingness of firms to hire workers.
B) is the same as the market demand curve for the product labor produces because it is a derived demand.
C) is determined by adding up the demand for labor by each firm at each wage, holding constant the other variables that affect the willingness of firms to hire workers.
D) is perfectly inelastic because there is a finite number of workers in the market for labor.