Final answer:
Collisions is considered a variable as it can vary depending on the circumstances.
Step-by-step explanation:
In the given options, the variable is the one that can vary or change. It is a quantity or characteristic that can take different values. Out of the given options, collisions is considered a variable because it can vary depending on the circumstances. For example, in a physics experiment, the number of collisions between particles may increase or decrease based on different factors. Therefore, collisions is the correct answer.
Learn more about Variables in Mathematics