Factor the Expression Completely $9 z ^ { 2 } + 42 z + 49$

Multiple Choice

Factor the expression completely. $9 z ^ { 2 } + 42 z + 49$

A) $\quad ( 3 z - 7 ) ^ { 2 }$
B) $\quad ( 3 z + 7 ) ( 3 z - 7 )$
C) $\quad 7 ( 3 z + 7 )$
D) $\quad ( 3 z + 7 ) ^ { 2 }$