A researcher wants to test whether people are more likely to donate to charity if they are in a good mood. Which of the following is one way the researcher could do this?
a. Show participants a graph depicting the donation rates of happy individuals.
b. Conduct interviews with individuals after they have donated to charity.
c. Ask participants to recall a recent time when they felt happy, then present them with a donation opportunity.
d. Offer participants a monetary reward for donating to charity.