This is an inference question. The answer is in the first paragraph, where the author discusses Marx. The author says "it has been said that no thinker has ever had his words more badly misrepresented, by supporters and detractors alike, than Karl Marx."
This supports choice C.
Choice A is a trap that goes too far. There is a difference between saying someone is "one of the most influential" and "the most influential."
Choice B is not a valid inference. Nothing in the passage suggests Marx spent "too much" time on economics, just that he was "especially concerned" with it.
Choice D is incorrect because the passage states that "Marx’s followers" launched an assault, not Marx.
Choice E uses some of the right words, but gets the meaning wrong. Marx’s views have been less than successful in describing global relations, not economics.