Social Psychologists Seldom Address the Question of External Validity by Conducting

Social psychologists seldom address the question of external validity by conducting their experiments on random samples of people from all over.This is because

A) human beings are incredibly complex, and social psychologists are content with doing inexact science.
B) the research methods that social psychologists use cannot be applied to a random sample.
C) it is difficult and expensive to get a random sample of people to participate in research.
D) social psychology is poorly funded, and experimenters are forced to do inexpensive research.
E) experiments capture general psychological processes experienced by people all over.