An Experimenter Is Studying the Facial Expression of the Emotion

An experimenter is studying the facial expression of the emotion terror. He plans to point a loaded gun at participants as they enter the room and photograph them at the same instant. Such an experiment would be ethically

A) acceptable if the experimenter explained the experiment afterward.
B) acceptable if the experimenter explained the experiment afterward and if the participants were paid.
C) acceptable if the participants were paid.
D) unacceptable because the risks and discomfort to the participants outweigh the potential benefits of the knowledge gained.