A Firm Combines Two Resources, a and B, to Produce

Multiple Choice

A firm combines two resources, A and B, to produce an output, Q. Their respective marginal revenue products are $30 and $21. A costs $15 a unit and B $7 a unit. To reduce the cost of Q,

A) more B and less A should be used.
B) more A and less B should be used.
C) more of both resources should be used.
D) less of both resources should be used.