Completely Factor the Expression Below $3 u + 7 u ^ { 2 } + 21 + u ^ { 3 }$

Multiple Choice

Completely factor the expression below. $3 u + 7 u ^ { 2 } + 21 + u ^ { 3 }$

A) $( u + 7 ) \left( 3 - u ^ { 2 } \right)$
B) $( u + 7 ) \left( 3 + u ^ { 2 } \right)$
C) $\left( u ^ { 2 } - 7 \right) ( 3 + u )$
D) $\left( u ^ { 2 } - 7 \right) ( 3 - u )$
E) $\left( u ^ { 2 } + 7 \right) ( 3 - u )$