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

Naomi got a slingshot for her birthday, and she was learning to use it by launching a rubber ball in a local park. Naomi noticed that the ball traveled farther when she pulled the sling back more. She wondered how much farther the ball would travel for each additional inch she pulled the sling back.
Naomi launched the ball from the slingshot six times and measured how far the ball traveled each time. On the first two launches, she pulled the sling back four inches. On the next two launches, she pulled the sling back five inches. On the final two launches, she pulled the sling back six inches.
Hint: An independent variable is a variable whose effect you are investigating. A dependent variable is a variable that you measure.
Figure: a slingshot pulled back.
Which of the following was an independent variable in this experiment?
A. the distance the sling was pulled back
B. the distance the ball traveled
Choose the right answer from the options and respond with its letter.

A