Four rods with different radii r and length l are connected to two reservoirs at different temperature. Which one of them will conduct most heat?

A

$$r = 2cm  \&  l = 2m$$

B

$$r = 1cm  \&  l = 1m$$

C

$$r = 2cm  \&  l = \frac{1}{2}m$$

D

$$r = \frac{1}{2}cm  \&  l = \frac{1}{2}m$$