Section: Science

78) Scientists performed an experiment to determine whether there is a connection between learning ability and food. They took two groups of 20 mice each, all from the same purebred strain. The mice were deprived of food for 3 days and then given a standard learning session in running through a maze. They were trained by giving them a mild electric shock whenever they took a wrong turn. Immediately after each learning session, one group of mice was fed, but the other was not, A week later, all of the mice were tested to see whether they could still run the maze correctly. The group that had been fed had retained this ability, but the other group had not.

The probable reason that the scientists used only mice from the same pure-bred strain is so that

1. the mice would all be the same size
2. the mice would all be the same color
3. the experiment could be repeated with the same mice
4. genetic differences would not affect the outcome of the test
5. the experiment wouldn’t cost as much

Neither size nor color was a factor in this experiment, nor was the cost an issue. The same mice could not be reused: the variable in this experiment is learning, and the mice had already been influenced.