Why Is Probability Theory Needed Rather Than Assuming That a Finding

Why is probability theory needed rather than assuming that a finding is different from that of the population?

A) Due to sampling variation a sample will always be at least slightly different from the population
B) To be 100% sure that our findings are correct
C) To say that our independent variable unquestionably causes the dependent variable
D) Confidence intervals are not enough to be certain of our findings