The ends of modern centuries have been greeted with both apocalyptic anxieties and utopian fantasies. It is not surprising that both reactions have consistently proven to be misplaced. After all, the precise time when a century happens to end cannot have any special significance, since the Gregorian calendar, though widely used, is only one among many that people have devised. Which one of the following, if true, could be substituted for the reason cited above while still preserving the force of the argument? ['The firm expectation that something extraordinary is about to happen can make people behave in a manner that makes it less likely that something extraordinary will happen.', 'Since a century far exceeds the normal human life span, people do not live long enough to learn from mistakes that they themselves made one hundred years before.', 'The number system based on the number ten, in the absence of which one hundred years would not have the appearance of being a significant period of time, is by no means the only one that people have created.', 'It is logically impossible for both reactions to be correct at the same time.']