Three conducting rods of same material and cross-section \( P \) ar...

Three conducting rods of same material and cross-section
\( P \) are shown in figure. Temperatures of \( \mathrm{A}, \mathrm{D} \) and \( \mathrm{C} \) are

W maintained at \( 20^{\circ} \mathrm{C}, 90^{\circ} \mathrm{C} \) and \( 0^{\circ} \mathrm{C} \). The ratio of lengths of \( \mathrm{BD} \) and \( \mathrm{BC} \) if there is no heat flow in \( \mathrm{AB} \) is
(a) \( 2 / 7 \)
(b) \( 7 / 2 \)
(c) \( 9 / 2 \)
(d) \( 2 / 9 \)