The correct answer is "C. all of history has been a struggle between classes of people."
Karl Marx was a German economist and socialist revolutionary who developed the theory of Marxism, which states that societies have developed a long time through class struggle. He attributes this to capitalism, where the ruling classes, which control the means of production enter in conflict with the working classes, also known as "the proletariat". This constant struggle would eventually lead to the fall of capitalism and the rise of a new system called socialism.