Simplify Assume That All Variables Represent Any Real Number $$\sqrt { x ^ { 2 } + 18 x + 81 }$$

Multiple Choice

Simplify. Assume that all variables represent any real number.
- $$\sqrt { x ^ { 2 } + 18 x + 81 }$$

A) $x + 9$
B) $- x - 9$
C) $| x + 9 |$
D) $- | x + 9 |$