Hexadecimal (base-16) numbers are written using numeric digits 0 through 9 as well as the letters A through F to represent 10 through 15. Among the first 1000 positive integers, there are n whose hexadecimal representation contains only numeric digits. What is the sum of the digits of n?<spanclass=′latex−bold′>(A)</span>17<spanclass=′latex−bold′>(B)</span>18<spanclass=′latex−bold′>(C)</span>19<spanclass=′latex−bold′>(D)</span>20<spanclass=′latex−bold′>(E)</span>21