Students Conducted a Naturalistic Observation to Study Whether People Arriving

Students conducted a naturalistic observation to study whether people arriving at the library alone would be more likely to hold the door open for a person coming in immediately after them than would people who arrived in pairs.The students made their observations looking through the window of a classroom building across from the library.They chose this position for observation to avoid the potential problem of

A) demand characteristics.
B) observer bias.
C) nonrepresentative sampling.
D) reactivity.