Find $a$ , Such That the Function $f ( x ) = 4 x + \sqrt { a - x ^ { 2 } }$

Multiple Choice

Find $a$ , such that the function $f ( x ) = 4 x + \sqrt { a - x ^ { 2 } }$ has the domain $( - 4,4 )$ .

A) $a = - 16$
B) $a = \sqrt { 4 }$
C) $a = - \sqrt { 4 }$
D) $a = 16$
E) $a = 4$