8. Dr. Ling is studying helping behavior in children. Every day, Dr. Ling goes to the local playground at 3 p.m., sits on the sidelines, and records the number of times one child helps another, the sex of the child who helps, and the sex of the child who is helped. Dr. Ling is using which research method in this study?

a. An experiment

b. A case study

c. A naturalistic observation

d. A quasi-experiment