Answer:
Make sure all tested rats are the same age.
Offer the same type of food to the rats in each trial.
Explanation:
In order to be able to isolate the effects of one particular variable during a research, all the subjects in each trial must be subjected to the same conditions except the variable whose effects is being isolated.
Hence, Kate must offer the same type of food to the rats in each trial as well as make sure that all tested rats are the same age.
