Simplify the Expression $\left( 7 x ^ { 8 } \right) ^ { 2 }$

Multiple Choice

Simplify the expression. $\left( 7 x ^ { 8 } \right) ^ { 2 }$

A) $7 x ^ { 16 }$
B) $7 x ^ { 8 }$
C) $49 x ^ { 17 }$
D) $49 x ^ { 16 }$
E) $49 x ^ { 15 }$