If the sum of any 10 of 21 real numbers is less than the sum of remaining 11 of them, at least how many of these 21 numbers are positive?<spanclass=′latex−bold′>(A)</span>18<spanclass=′latex−bold′>(B)</span>19<spanclass=′latex−bold′>(C)</span>20<spanclass=′latex−bold′>(D)</span>21<spanclass=′latex−bold′>(E)</span>None of the preceding