For how many primes p less than 15, there exists integer triples (m,n,k) such that
m+n+kmn+mk+nkmnk≡≡≡0(modp)1(modp)2(modp).<spanclass=′latex−bold′>(A)</span>2<spanclass=′latex−bold′>(B)</span>3<spanclass=′latex−bold′>(C)</span>4<spanclass=′latex−bold′>(D)</span>5<spanclass=′latex−bold′>(E)</span>6