Answer:
D. naturalistic observation
Step-by-step explanation:
Naturalistic observation is a method of research that consists in observing subjects in their natural environment without any exterior interferences that could alter their behavior. By posing as a student, Dr. Jimand is inserting himself among the other students to observe their natural behavior. For instance, if they were told that there was a doctor observing them, the students' behavior could change and that wouldn't be a true naturalistic observation.