In the context of the author's argument, the last sentence performs which of the following functions? A. It explains a criterion that was employed earlier in the argument. B. It shows that an apparently plausible position is actually self-contradictory. C. It is a conclusion drawn in the course of refuting a potential explanation. D. It overturns an assumption on which an opposing position depends. E. It states the main conclusion that the author is seeking to establish.