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

• A. \[r=2{{r}_{0}};\ l=2{{l}_{0}}\]
• B. \[r=2{{r}_{0}};\ l={{l}_{0}}\]
• C. \[r={{r}_{0}};\ l={{l}_{0}}\]
• D. \[r={{r}_{0}};\ l=2{{l}_{0}}\]