A scientist designs an experiment to test how the intensity or strength of light affects plant growth which of the following should be consistent among the plants he test Mark all that apply

The variables that must be kept constant in different subjects of an experiment are known as controlled variables. These variables are those that may affect the experiment's outcome, so they are kept the same for each of the trials.

In this example, the amount of water the plants receive, the size of their pots and the amount of soil in the pots are all variables that must be controlled.