Simplify and Write with Positive Exponents Only $\frac { x ^ { 3 } } { x ^ { 7 } }$

Simplify and write with positive exponents only.
- $\frac { x ^ { 3 } } { x ^ { 7 } }$

A) $\frac { 1 } { x ^ { 21 } }$
B) x¹⁰
C) x⁴
D) $\frac { 1 } { x ^ { 4 } }$