Completely Factor the Polynomial or State That the Polynomial Is $$x ^ { 4 } + 4 x ^ { 2 } - 21$$

Multiple Choice

Completely factor the polynomial or state that the polynomial is prime.
- $$x ^ { 4 } + 4 x ^ { 2 } - 21$$

A) $\left( x ^ { 2 } + 3 \right) \left( x ^ { 2 } + 7 \right)$
B) $\left( x ^ { 2 } - 3 \right) \left( x ^ { 2 } + 7 \right)$
C) prime
D) $\left( x ^ { 2 } + 3 \right) \left( x ^ { 2 } + 1 \right)$