Which of the following circular rods (given : radius rand length l) each made of the same material and whose ends are maintained at the same temperature will conduct most heat ?

• A

  $\mathrm{r}=2{\mathrm{r}}_0 ,\mathrm{l}=2{\mathrm{l}}_0$

• B

  $\mathrm{r} = 2{\mathrm{r}}_0 , \mathrm{l}= {\mathrm{l}}_0$

• C

  ${\text{r= r}}_0, \mathrm{l}= 2{\mathrm{l}}_0$

• D

  $\mathrm{r} = {\mathrm{r}}_0 ,\mathrm{l} ={\mathrm{l}}_0$