Find the Constant $a$ Such That the Function $f ( x ) = \left\{ \begin{array} { r r } - 4 \cdot \frac { \sin x } { x } , & x < 0 \\a + 7 x , & x \geq 0\end{array} \right.$

Multiple Choice

Find the constant $a$ such that the function
$f ( x ) = \left\{ \begin{array} { r r } - 4 \cdot \frac { \sin x } { x } , & x < 0 \\a + 7 x , & x \geq 0\end{array} \right.$ is continuous on the entire real line.

A) 1
B) $- 7$
C) $7$
D) $4$
E) $- 4$