Jane sets up an experiment to find out if kittens prefer skim milk, 2% milk, or whole milk. She puts out a cup of skim milk for 5 kittens and then measured how much the kittens drank during a day. The next day, she used the same kittens and put out a cup of 2% milk. The last day, she used the same kittens and put out a cup of whole milk. She discovered that the kittens preferred whole milk. There are many problems with this experiment. Each of the following would improve the experiment except which one?