Use the Properties of Exponents to Simplify the Expression $\left( e ^ { - 4 } \right) \left( e ^ { - 7 / 2 } \right)$

Multiple Choice

Use the properties of exponents to simplify the expression $\left( e ^ { - 4 } \right) \left( e ^ { - 7 / 2 } \right)$ .

A) $e ^ { - 14 }$
B) $e ^ { 55 }$
C) $e ^ { 14 }$
D) $e ^ { - 55 }$
E) $e ^ { 16 }$