$f ( x ) = \left\{ \begin{array} { c l } \frac { \sin ( a + 2 ) x + \sin x } { x } & ; x < 0 \\ b & ; x = 0 \\ \frac { \left( x + 3 x ^ { 2 } \right) ^ { 1 / 3 } - x ^ { 1 / 3 } } { x ^ { 1 / 3 } } & ; x > 0 \end{array} \right.$ is continuous at $x = 0$, then $a + 2 b$ is equal to:\\
(1) 1\\
(2) - 1\\
(3) 0\\
(4) - 2