$\left (x^{n}+a^{n} \right)$ is divisible by $(x+a)$ :

(x^n - a^n) is divisible by (x - a) for all values of n.

(x^n - a^n) is divisible by (x + a) for even values of n.

(x^n + a^n) is divisible by (x + a) for odd values of n.

ANSWER:C