Read the following paragraph and cross out TWO irrelevant sentences.

Every day in the United States some five thousand people reach the age of sixty-five. On that day they are not any physically or mentally different than the day before, but now they are assumed to be old. Who is thought of as old varies from society to society. Yet the use of age sixty-five as a criterion is not that relevant, for there is too much individual difference in mental capacity and physical endurance. So reaching sixty-five is a convenient but inaccurate indicator of being old. It is significant, however, because it labels people. People expect certain behaviors of others depending on their stage in the life cycle. If people define sixty-five as old, then they treat those who are sixty-five as old. In the process of aging the skin dries out, powers of seeing and hearing diminish, hair turns white and is gradually lost. In this way the expectations of society become a self-fulfilling prophecy(预言).