Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: In an investigation, a student wants to see how a ball is affected by rolling it over a surface covered with sandpaper. In preparation for the trial, the student makes a list of the possible conditions that could affect the investigation. The student is most likely listing the
variables.
variables.