By definition, r! \equal{} r(r \minus{} 1) \cdots 1 and \binom{j}{k} \equal{} \frac {j!}{k!(j \minus{} k)!}, where r,j,k are positive integers and k<j. If (1n),(2n),(3n) form an arithmetic progression with n>3, then n equals
<spanclass=′latex−bold′>(A)</span>5<spanclass=′latex−bold′>(B)</span>7<spanclass=′latex−bold′>(C)</span>9<spanclass=′latex−bold′>(D)</span>11<spanclass=′latex−bold′>(E)</span>12