Fill in the Blank with One of the Words or Phrases

Fill in the blank with one of the words or phrases listed below. Not all choices will be used. $$\begin{array} { l l l l } \text { least common denominator } & \text { simplifying } & \text { reciprocals } & \text { numerator } \\\text { cross products } & \text { ratio } & \text { proportion } & \text { denominator } \\\text { rational expression } & \text { domain } & \text { complex fraction } & \\\frac { - a } { b } & \frac { a } { - b } & \frac { - a } { - b } &\end{array}$$
-For a rational expression, $-\frac{\mathrm{a}}{\mathrm{b}}$ = ____= ____

A) $\frac { - \mathrm { a } } { \mathrm { b } } , \frac { - \mathrm { a } } { - \mathrm { b } }$
B) numerator, denominator
C) $\frac { - a } { b } , \frac { a } { - b }$
D) $\frac { - a } { - b } , \frac { a } { - b }$