Factor Completely Using the Grouping Method to Factor Trinomials $x ^ { 4 } - 4 x ^ { 3 } - 21 x ^ { 2 }$

Multiple Choice

Factor completely using the grouping method to factor trinomials. If unfactorable, indicate that the polynomial is prime.
- $x ^ { 4 } - 4 x ^ { 3 } - 21 x ^ { 2 }$

A) $x ^ { 2 } ( x + 3 ) ( x - 7 )$
B) $x ^ { 2 } ( x - 3 ) ( x - 7 )$
C) $x ^ { 3 } \left( x ^ { 2 } - 4 x - 21 \right)$
D) $x ^ { 2 } ( x + 3 ) ( x + 7 )$