AHSME 1969 Problem 7

If the points $(1,y_1)$ and $(-1,y_2)$ lie on the graph of $y=ax^2+bx+c$, and $y_1-y_2=-6$, then $b$ equals: $\text{(A) } -3 \text{(B) } 0 \text{(C) } 3 \text{(D) } \sqrt{ac} \text{(E) } \frac{a+c}{2}$