The Diagram Below Shows the MRP Curve for a Firm

The diagram below shows the MRP curve for a firm producing copper plumbing pipe.The factor of production being considered here is hours of labour. FIGURE 13-1
-Refer to Figure 13-1.This firm's MRP curve is the firm's

A) derived demand for copper plumbing pipe.
B) demand curve for labour.
C) market demand curve for copper plumbing pipe.
D) marginal product of labour curve.
E) total product curve for labour.