If two rods $\mathrm{A}$ and $\mathrm{B}$ of equal length $L$, and different areas of cross-section $A_{1}$ and $A_{2}$ have one end each at temperature $T_{1}$ and $T_{2}$, have equal rates of flow of heat, then:
(a) $A_{1}=A_{2}$
(b) $\frac{A_{1}}{A_{2}}=\frac{K_{2}}{K_{1}}$
(c) $\frac{A_{1}}{A_{2}}=\frac{K_{1}}{K_{2}}$
(d) $K_{1}=K_{2}$