Elizabeth will need a scale to measure the weight of the apples. This way she will determine whether the mass of the apples has increased or not.
Elizabeth should have a group of apple trees where the additives have been added to the soil, and a control group of apple trees where no additives have been added to the soil. In order to determine whether the soil additives have increased the mass of the apples, she needs to measure apples from both the control group and the group where the soil additives have been added.
