A Firm Uses Two Inputs, a and B $\mathrm{P}_{\mathrm{A}}$

Multiple Choice

A firm uses two inputs, A and B.At its optimal choice of input proportions,

A) MRP of A = MRP of B.
B) MR $\mathrm{P}_{\mathrm{A}}$ / $\mathrm{P}_{\mathrm{A}}$ = MR $\mathrm{P}_{\mathrm{B}}$ / $\mathrm{P}_{\mathrm{B}}$ .
C) MPP of A = MPP of B.
D) All of the above are correct.