On your visit to New York City, you and your friend observed that the grey rats (Rattus norvegicus) in the New York subway are considerably larger than a typical West Coast rat. You decided to test whether this difference was genetic or environmental. You obtained a litter of 10 New York rat pups, and a litter of 10 California rat pups. Each of you took 5 pups from each litter and kept them in your room for 3 months, despite your roommates' protests. You fed your rats a balanced diet of dry cat food and fresh fruit and vegetables. Your friend, however, has a soft heart and gave her rats french fries, cheeseburger wraps, hot dogs, and other nostalgic New York fare. At the end of your experiment, you found that the New York and California rats that grew up in your home were exactly the same size. Your friend, however, found that her New York rats were larger than her California rats, and both were larger than your rats. So, is the difference genetic or environmental? Explain why you concluded this.

a. Genetic
b. Environmental
c. Genotype environment interaction
d. a and b
e. b and c
f. a and c
g. a, b, and c