Use the Properties of Fractions to Simplify the Expression $\underline {\text { kilometers }}$

Use the properties of fractions to simplify the expression. $\underline {\text { kilometers }}$
$\underline {\text {kilometers }}$
$\underline {\text {second }}$

A) kilometers
B) $\frac{\text { kilometers } ^2}{\text { second } }$
C) second
D) $\frac { \text { second } } { \text { kilometer } }$
E) kilometers²