设函数 $f(x) = \frac{\sin x}{1 + x^2}$ 在 $x = 0$ 处的3次泰勒多项式为 $ax + bx^2 + cx^3$ ，则（ ）. (A) $a = 1, b = 0, c = -\frac{7}{6}$ $(\mathrm{B})a = 1,b = 0,c = \frac{7}{6}$ (C) $a = -1, b = -1, c = -\frac{7}{6}$ $(\mathrm{D})a = -1,b = -1,c = \frac{7}{6}$