Simplify the Expression $\sqrt { 2 x ^ { 3 } } - \sqrt { 18 x ^ { 3 } }$

Multiple Choice

Simplify the expression. All variables represent positive numbers. $\sqrt { 2 x ^ { 3 } } - \sqrt { 18 x ^ { 3 } }$

A) $- x \sqrt { 3 x }$
B) $- x \sqrt { 2 x }$
C) $- 2 x \sqrt { 2 x }$
D) $- 2 x \sqrt { 3 x }$
E) $- 2 x \sqrt { 5 x }$