Factor Completely $$9 x ^ { 4 } + 21 x ^ { 3 } - 9 x ^ { 2 } - 21 x$$

Multiple Choice

Factor completely.
- $$9 x ^ { 4 } + 21 x ^ { 3 } - 9 x ^ { 2 } - 21 x$$

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