Simplify Assume That Variables in the Exponent Represent Nonzero Integers $\left( x ^ { a } + 9 \right) ^ { 7 }$

Multiple Choice

Simplify. Assume that variables in the exponent represent nonzero integers and that all other variables are not 0.
- $\left( x ^ { a } + 9 \right) ^ { 7 }$

A) $x ^ { a } + 63$
B) $x ^ { 7 } a + 63$
C) $x ^ { a } + 16$
D) $7 x ^ { a } + 9$