Which of the Following Is a Common Reason That Researchers

Which of the following is a common reason that researchers often use samples to test a theory?

A) Populations are often not representative of all the relevant cases needed to test a theory.
B) Actual data can be gathered only from samples; populations are merely theoretical.
C) It is often not feasible to collect data from every case in the population.
D) Populations are often too small to accurately test a theory.