Use Properties of Rational Exponents to Simplify the Expression $\frac { x ^ { 1 / 3 } } { x ^ { 6 / 7 } }$

Multiple Choice

Use properties of rational exponents to simplify the expression. Assume that any variables represent positive numbers.
- $\frac { x ^ { 1 / 3 } } { x ^ { 6 / 7 } }$

A) $\frac { 1 } { \mathrm { x } ^ { 11 / 21 } }$
B) $x ^ { 25 / 21 }$
C) $x ^ { 7 / 18 }$
D) $x ^ { 11 / 21 }$