For functions f and g defined on the set of real numbers
$$\begin{aligned}
& f ( g ( x ) ) = x ^ { 2 } + 4 x - 1 \\
& g ( x ) = x + a \\
& f ^ { \prime } ( 0 ) = 1
\end{aligned}$$
Given this, what is a?
A) $-2$\\
B) $\frac { -1 } { 4 }$\\
C) 1\\
D) $\frac { 3 } { 2 }$\\
E) 3