Simplify the Expression $$\sqrt { x ^ { 2 } - 14 x + 49 }$$

Multiple Choice

Simplify the expression.
- $$\sqrt { x ^ { 2 } - 14 x + 49 }$$

A) $x + 7$
B) $x - 7$
C) $| ( x - 7 ) ( x + 7 ) |$
D) $| x - 7 |$