Scientists conducted the experiment to find out whether there is a connection between learning ability and food. They took two groups of 20 mice each, all from same purebred strain. Mice were deprived of food for 3 days and then given standard learning session in running through maze. They were trained by giving them mild electric shock whenever they took wrong turn. Immediately after each learning session, one group of mice was fed, but other was not, week later, all the mice were tested to see whether they could still run maze correctly. Group that had been fed had retained this ability, but other group had not. Probable reason that scientists used only mice from same pure-bred strain is so that?

A) experiment could be repeated with same mice
B) genetic differences would not affect outcome of test
C) mice would all be same color
D) mice would all be same size