Context: The passage below describes an experiment. Read the passage and think about the variables that are described.

Katy liked to make guacamole, but she could often find only unripe  at the grocery store. In biology class, Katy learned that ripe fruits produce a gas called ethylene that can cause other fruits to ripen. Katy wondered whether storing ripe bananas with unripe  would make the  ripen faster.
Katy prepared four paper bags with five unripe  in each bag. She added one ripe banana to two of the bags and no bananas to the remaining two bags. Then, Katy sealed all four bags. After three days, she opened each bag and counted the number of ripe  in each bag.
Hint: An independent variable is a variable whose effect you are investigating. A dependent variable is a variable that you measure.
Figure: avocados.
Which of the following was an independent variable in this experiment?
A. the number of ripe bananas
B. the number of ripe avocados
Choose the right answer from the options and respond with its letter.

A