From some observations, a student noticed there are fruit flies flying around and landing on a banana in the kitchen. The student wondered if a certain type of fruit will attract more fruit flies than another. The student set up four jars of the exact same size on the countertop in an area where the light remains the same. They weighed the following fruits and placed 110 grams of each fruit into the jars: banana, strawberry, peach, watermelon. The student had 4 vials of fruit flies (all female, same species, same number) and placed each vial directly in front of jar. The student asked a friend to take the cover off of two of the vials while they removed the other covers simultaneously. An hour later the student recorded the number of fruit flies in each jar and continued to record data every twelve hours for 5 days in a row. In this experiment, what is the independent variable?
Question 1 options:

The number of flies in each jar.

The different types of fruit.

The jars, countertop and species of fruit fly.

The time of day the experiment was set up.