Answer:
-using seeds from the same source
-using the same kind of soil for both groups
-giving the control and experimental groups the same volume of water
-keeping the light the same for the experimental and control groups
-measuring plant height the same way and at the same time for both groups
Step-by-step explanation:
Using seeds from the same source makes sure that the seeds are of the same species, and using the same soil prevents one group from growing faster or slower because of increased initial nutrition. The same amount of water was also used so that the plants wouldn't die or grow more quickly solely because of water. And, finally, accurate measurements were taken to minimize the chance of incorrect information.