3. Given the quadratic function
$$
y=a x^{2}+b x+c
$$

the graph is as shown in the figure, then among the following 6 algebraic expressions $a b, a c, a+b+c, a-b+c$, $2 a+b, 2 a-b$, the number of expressions with positive values is
(A) 2;
(B) 3;
(C) 4;
(D) More than 4.
3. (A)

Solution The graph opens downwards, so $a<0$, $2a+b<0$, $a-b+c<0$. Among the 6 given algebraic expressions, only 2 are positive.