The function $f(x)=b{x}^2+dx+e$, where $b$ and $e$ are constants, is a quadratic function whose graph in the $xy$-plane is a parabola that opens upward and has a vertex at $(h,k)$. If $k>0$and $f(-6)=f(2)$, which of the following must be true?
I. $d>0$
II. $e<k$