7. There exists a function $f ( x )$ satisfying, for all $x \in \mathbb{R}$, A. $f ( \sin 2 x ) = \sin x$ B. $f ( \sin 2 x ) = x ^ { 2 } + x$ C. $f \left( x ^ { 2 } + 1 \right) = | x + 1 |$ D. $f \left( x ^ { 2 } + 2 x \right) = | x + 1 |$
7. There exists a function $f ( x )$ satisfying, for all $x \in \mathbb{R}$,\\
A. $f ( \sin 2 x ) = \sin x$\\
B. $f ( \sin 2 x ) = x ^ { 2 } + x$\\
C. $f \left( x ^ { 2 } + 1 \right) = | x + 1 |$\\
D. $f \left( x ^ { 2 } + 2 x \right) = | x + 1 |$