设$f(x)$二阶可导,且$f(0)=0$,令 $g(x)= \begin{cases} \frac {f(x)}{x},&x \neq 0, \\ f'(0),&x=0. \end{cases}$
(1)求 $g'(x)$;(2)讨论$g'(x)$在$x=0$处的连续性.
$\text{A.}$ 若 $\lim \limits _{x \rightarrow 0^{ }}f(x)=0$, 则 $\lim \limits _{x \rightarrow 0^{ }}f'(x)=0$
$\text{B.}$ 若 $\lim \limits _{x \rightarrow 0^{ }}f'(x)=0$, 则 $\lim \limits _{x \rightarrow 0^{ }}f(x)=0$
$\text{C.}$ 若 $\lim \limits _{x \rightarrow \infty }f(x)= \infty $, 则 $\lim \limits _{x \rightarrow \infty }f'(x)= \infty$
$\text{D.}$ 若 $\lim \limits {x \rightarrow \infty }f'(x)=A>0$, 则 $\lim \limits {x \rightarrow \infty }f(x)= \infty$