The researcher responsible for discovering classical conditioning was __________

Studies of the immune system in animals have found that stressors such as crowding

a. can lead to increased levels of immune system activity. b. can activate the release of aggressive pheromones. c. can increase levels of serotonin and dopamine. d. can reduce various aspects of immune system activity.

Which of the following are the two general designs used by human development researchers?

a. experimental studies and quasi-experimental studies b. observational studies and self-report studies c. case studies and self-report studies d. correlational studies and experimental studies