If $\lim\limits_{x\to \infty}\big(\large\frac{x^3+1}{x^2+1}$$-(ax+b)\big)=2$ then

Question

$\begin{array}{1 1}(a)\;a=1,b=1&(b)\;b=1,b=2\\(c)\;a=1,b=-2&(d)\;None\;of\;these\end{array}$