173- In the figure shown, two conducting rods are placed between two heat sources. If the cross-sectional area of rod A is $\frac{1}{2}$ the cross-sectional area of rod B, and the thermal conductivity of rod A is 6 times the thermal conductivity of rod B, what is the ratio of the thermal conduction rate in rod A to the thermal conduction rate in rod B?
\begin{minipage}{0.45\textwidth}
[Figure: Two rods A and B connected between heat sources $T_1$ and $T_r \neq T_1$] \end{minipage} \begin{minipage}{0.45\textwidth}
- [(1)] $2$
- [(2)] $4(2)$
- [(3)] $\dfrac{1}{2}$
- [(4)] $\dfrac{1}{4}$
\end{minipage}
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