Respuesta :
Answer:
One.
Explanation:
In a scientific experiment, you should only change one factor, or variable, at a time. All the other factors need to stay the same, or constant. If you change more than one factor at a time, you won't be able to tell which factor is the reason for the change in results.
the factor that is purposely changed by the experimenter; the factor the experimenter decides to change . ... What did the experimenter change on purpose? The level of the independent variable. The changes that are made in the dependent variable. So One )