In a large lecture hall, students were handed a drawing of a woman. Students didn’t know that those on the left side of the center aisle received a drawing of a young woman while those on the right side of the aisle were given a drawing of an old woman. A slide was then projected with an drawing that was an ambiguous combination of the two handouts and students were asked a series of questions.

This is an example of which of the following?

A. A blind observational study
B. An observational study that isn’t blind
C. A blind experiment
D. An experiment that isn’t blind