If You Are Conducting Research That Involves Making Observations of People's

If you are conducting research that involves making observations of people's behaviour,one major issue that you would need to be concerned about is:

A) that people may behave differently when they know they are being watched.
B) that if you do not have a representative sample,then your observations will be confounded.
C) that people's behaviours often do not have good internal validity.
D) that you must consider at least two different variables in order to draw cause-and-effect conclusions.