A scientist testing the effects of a chemical on apple yield sprays an orchard with the chemical. A second orchard does not receive the chemical. In the fall, the number of apples harvested from each forest is counted.
Which of the following is the independent variable in the experiment?
1.the amount of water that each orchard receives
2. the species of trees in the orchard
3.the number of apples that are produced by each tree
4.the size of each of the orchards