All of the following are issues with animal research involving animals bred in a breeding colony, but which one might decrease the external validity of your study? 1) since all animals are bred and raised in the same environment, they may differ from animals bred in a different colomy 2) animal activists may find it unethical to use animals in research 3) working with animals requires irb protocols that safeguard the well-being of the animals, making it impossible to perform some experiments on them 4) all of the above can decrease the external validity of a study