In preparation for his master’s thesis, Tan spends some time in the local mall observing the behavior of shoppers. His notes reveal a tendency for people to smile when someone, even a stranger, smiles at them. Later in the semester, he designs a questionnaire that asks questions of participants concerning their typical reactions when someone smiles. He wonders if the face of a person who smiles has any influence on returned smiles, so he designs a study to answer this question. Which of the following lists in order, from first to last, the research methods Tan has used?

a) experiment, case study, survey

b) case study, survey, experiment

c) correlation, case study, experiment

d) naturalistic observation, survey, experiment