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

Bryce noticed that some of the footballs his team used during practice were not fully inflated. He wondered whether fully inflated footballs would travel farther than footballs with a lower air pressure.
To find out, Bryce collected 20 standard footballs. He fully inflated ten of them to an air pressure of 13 pounds per square inch. He inflated the remaining ten to an air pressure of 10 pounds per square inch. Bryce used  to launch a ball across a football field. He measured the distance the football traveled and then launched the next ball. Bryce repeated this with all 20 balls.
Hint: An independent variable is a variable whose effect you are investigating. A dependent variable is a variable that you measure.
Figure: a football launcher.
Which of the following was an independent variable in this experiment?
A. the distance the footballs traveled
B. the air pressure in the footballs
Determine the correct option from the provided choices and reply with its corresponding letter.

B