3. If the solution set of the inequality $a x^{2}+b x+4>0$ is $\{x \mid-2<x<1\}$, then the maximum and minimum values of the quadratic function $y=b x^{2}+4 x+$ $a$ on the interval $[0,3]$ are ( ).
(A) $0,-8$
(B) $0,-4$
(C) 4,0
(D) 8,0
3. A.

From the problem, we know that $a<0$ and the quadratic equation $a x^{2}+b x+4=0$ has two roots, -2 and 1. Therefore, $-\frac{b}{a}=-1, \frac{4}{a}=-2$. Hence, $a=-2, b=-2$. So, the quadratic function $y=b x^{2}+4 x+a$ has a maximum value of 0 and a minimum value of -8 on the interval $[0,3]$.