What Are the Two Requirements for Evaluating the Accuracy of a Set

What are the two requirements for evaluating the accuracy of a set of observations

A) the data must be observed values, and it must be possible to measure these events directly
B) the data must represent physical events, and it must be possible to measure these events directly
C) the data must represent physical events, and they must be true values
D) the data must be true values, and they must be able to be measured using direct assessments