Multiply Using One of the Rules for the Square of a Binomial

Multiple Choice

Multiply using one of the rules for the square of a binomial. Assume any variable exponents represent whole numbers.
- $$\left( a ^ { n } + 3 b ^ { n } \right) ^ { 2 }$$

A) $a ^ { 2 n } + 6 a ^ { n } b ^ { n } + 9 b ^ { 2 n }$
B) $a ^ { n } + 6 a ^ { n } b ^ { n } + 9 b ^ { n }$
C) $a ^ { n + 2 } + 6 a ^ { n } b ^ { n } + 9 b ^ { n + 2 }$
D) $a ^ { 2 n } + 3 a ^ { n } b ^ { n } + 9 b ^ { 2 n }$