Answer:
When only one factor is changed, you can be more certain that it caused the results.
Explanation:
A controlled experiment is usually performed to determine the effect of a certain factor. If more than one factor is changed in a single experiment, then we won't be able o determine which factor was responsible for bringing the change in our experiment. Hence, it is important that in controlled experiments, we study one factor at a time. Study of more than one factor will not give reliable results.
