即：1/(ax²+bx+c)是1/(x+1)的高阶无穷小lim [1/(ax²+bx+c)]/[1/(x+1)]=0x→∞lim (x+1)/(ax²+bx+c)]=0x→∞lim (1+ 1/x)/(ax+ b +c/x)]=0x→∞lim 1/(ax+ b)=0x→∞a≠0a≠0，b、c为任意常数。选C
