A Solution Of $y ^ { \prime \prime } + 9 y = 0$

Multiple Choice

A solution of $y ^ { \prime \prime } + 9 y = 0$ is

A) $y = 3 \sin ( 3 x )$
B) $y = \sin ( 3 x )$
C) $y = - \sin ( 3 x )$
D) $y = \cos ( 3 x )$
E) All of the above