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

Question

( A ) $r=r_0;l=l_0$
( B ) $r=2r_0;l=2l_0$
( C ) $r=r_0;l=2l_0$
( D ) $r=2r_0;l=l_0$