If k is a positive number and f is a function such that, for every positive number x, [f(x2+1)]x=k; then, for every positive number y, [f(y29+y2)]y12 is equal to<spanclass=′latex−bold′>(A)</span>k<spanclass=′latex−bold′>(B)</span>2k<spanclass=′latex−bold′>(C)</span>kk<spanclass=′latex−bold′>(D)</span>k2<spanclass=′latex−bold′>(E)</span>yk