Among the theories of knowledge, empiricism as a way of reaching-knowledge, the basic assumption is that true knowledge can only be acquired through senses and observations. So, empiricists don’t accept a priori knowledge. Positivism is distinguished by four important assumptions. First of these is the belief about the uniqueness of science. According to this assumption which is called as naturalism in philosophical language, there is no important difference between natural world and social world and through the methodology of natural science, social world can be analyzed. Second assumption is that there should be a distinction between facts and values. In terms of philosophy, this point of view which is known as objective position assumes that objective knowledge can be attained by scientific methods despite the existence of subjective factors influencing the research. Third assumption is based on the belief that as in the universe or natural world, there are also regularities in the social world. In this way, as research is carried out, either deductive or inductive methods are employed. According to the final assumption, research must be based on the methods of empirical verification or falsification. The answer is D.