Factor the Expression Over the Set of Complex Numbers $4 a ^ { 2 } + 9$

Multiple Choice

Factor the expression over the set of complex numbers $4 a ^ { 2 } + 9$

A) $\quad ( 2 + 3 i ) ( 2 - 3 i )$
B) $\quad ( 2 a + 3 ) ( 2 a - 3 )$
C) $\quad ( - 2 a + 3 i ) ( - 2 a + 3 i )$
D) $\quad ( 2 a + 3 i ) ( 2 a - 3 i )$
E) $\quad ( 2 a + 3 i ) ( 2 a + 3 i )$