Simplify the Radical Expression $$\sqrt { 9 x ^ { 2 } + 18 x + 9 }$$

Multiple Choice

Simplify the radical expression. If appropriate, include absolute values.
- $$\sqrt { 9 x ^ { 2 } + 18 x + 9 }$$

A) $- 3 x + 6$
B) $3 x + 3 + \sqrt { 18 x }$
C) $| 3 x + 3 |$
D) $| 3 x - 3 |$