Emma, a psychologist, wants to study the relationship that exists among female college students who stay in hostels. She disguises herself as a college student and shares a dorm with some of the students for a month. During her stay, she observes their various behaviors and makes notes when they are asleep. Which of the following is best exemplified in this scenario?

a. naturalistic observation
b. the placebo effect
c. experimenter blas
d. a double-blind experiment