(2)设 (x)=lim _(narrow infty )dfrac ({x)^2n-1+a(x)^2+bx}({x)^2n+1} 若 =1, x=-1 均为f(x)的跳跃间断点,则 () ()-|||-(A) +b=1, -bneq -1 (B) +b=1, a-b=-1-|||-(C) +bneq 1, -bneq -1 (D) +bneq 1, a-b=-1