(1)设函数$y=y(x)$由 $\begin{cases} x= \arctan t, \\ y= \ln (1 t^{2}) \end{cases} $确定，求 $\dfrac {dy}{dx}$, $\dfrac {d^{2}y}{dx^{2}}$.
(2)设函数$y=y(x)$由 $\begin{cases} x=1 t^{2}, \\ y= \sin 2t \end{cases}$ 确定，求 $\dfrac {dy}{dx}$, $\dfrac {d^{2}y}{dx^{2}}$.
$\text{A.}$ $f(x)= \dfrac {|x|}{x 1}$
$\text{B.}$ $f(x)= \sqrt { \cos x}$
$\text{C.}$ $f(x)=x \arctan \dfrac {1}{x}$
$\text{D.}$ $f(x)= \cos \sqrt {|x|}$