Historian: Political regimes that routinely censor various forms of expression on the grounds that they undermine public morality inevitably attempt to expand the categories of proscribed expression to include criticisms that these regimes perceive to threaten their power. Accordingly, many totalitarian regimes classify as blasphemous or pornographic those writings that would, if widely influential, reduce public passivity. Which one of the following is an assumption on which the historian's reasoning depends? ['Most writings that totalitarian regimes label blasphemous or pornographic would, if widely influential, reduce public passivity.', 'Not all political regimes that routinely censor forms of expression on the grounds that they erode public morality are totalitarian regimes.', 'A totalitarian regime can perceive loss of public passivity as a threat to its power.', 'Widespread public passivity is usually needed for a regime to retain political power.']