The correct answer is D.
Economists prove their claims by testing a set of hypothesis, based on a previous and exhaustive study undertaken on a certain matter, through the collection of empirical data. The initial hypothesis will be tested using such data to reach a conclusion: the hyphotesis are either accepted or rejected.
Apart from population statistics, by using econometric techniques, it is possible to conduct inference on sample data, which yields appropiate statistics to study a whole population.
