AHSME 1968 Problem 13

If $m$ and $n$ are the roots of $x^2+mx+n=0 ,m \ne 0,n \ne 0$, then the sum of the roots is: $\text{(A) } -\frac{1}{2} \text{(B) } -1 \text{(C) } \frac{1}{2} \text{(D) } 1 \text{(E) } \text{undetermined}$