Fill in the Blank with One of the Words or Phrases

Multiple Choice

Fill in the blank with one of the words or phrases listed below. $\begin{array}{llll}\text { mixed number } & \text { equivalent } & 0 & \text { undefined } \\\text { composite number } & \text { improper fraction } & \text { simplest form } & \text { prime factorization } \\\text { prime number } & \text { proper fraction } & \text { numerator } & \text { denominator }\\\text { reciprocals } & \text { cross products }\end{array}$
-InIn $\frac { a } { b } = \frac { c } { d ^ {} },$ , a a· d and b · c are called___________ .

A) cross products
B) prime factorization
C) reciprocals
D) simplest form