Cho hàm số $f(x)=\left\{ \begin{array}{l}\frac{{{x}^{2}}+1}{1-x}\,\,\,\,\,\,\,khi\,x<1\\\sqrt{2x-2}\,\,khi\,x\ge 1\end{array} \right.$ . Khi đó$\displaystyle \underset{x\to {{1}^{-}}}{\mathop{\lim }}\,f\left( x \right)$ là
A. $\displaystyle +\infty .$
B. $-1.$
C. $0.$
D. $1.$
