Find All Solutions of the Equation $$x ^ { 4 } + 16 i = 0$$

Find all solutions of the equation. Leave answers in trigonometric form.
- $$x ^ { 4 } + 16 i = 0$$

A) $\left\{ \operatorname { cis } \frac { 3 \pi } { 8 } , \operatorname { cis } \frac { 7 \pi } { 8 } , \operatorname { cis } \frac { 11 \pi } { 8 } , \operatorname { cis } \frac { 15 \pi } { 8 } \right\}$
B) $\left\{ 16 \operatorname { cis } \frac { 3 \pi } { 8 } , 16 \operatorname { cis } \frac { 7 \pi } { 8 } , 16 \operatorname { cis } \frac { 11 \pi } { 8 } , 16 \operatorname { cis } \frac { 15 \pi } { 8 } \right\}$
C) $\left\{ 2 \operatorname { cis } \frac { 3 \pi } { 8 } , 2 \operatorname { cis } \frac { 7 \pi } { 8 } , 2 \operatorname { cis } \frac { 11 \pi } { 8 } , 2 \operatorname { cis } \frac { 15 \pi } { 8 } \right\}$
D) $\{ 1 , - 1 , i , - i \}$