Problem: Researchers want to explore whether the size of gonads in female fruit flies is tied to food availability during early development. They raise two batches of flies, one raised on a normal food ration, one raised on a restricted food ration. Because fly gonads are tiny and hard to measure, gonad size is classified into one of three levels: absent, small, large. What is the response variable in this study?
a. food ration
b. study duration
c. none of these
d. researcher bias
e. gonad size