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?