根据材料请回答 46～50 题 The Process of AgeingAt the age of twelve years, the human body

根据材料请回答 46～50 题

The Process of Ageing

At the age of twelve years, the human body is at its most vigorous.It has yet to reach its full size and strength, and its owner his or her full intelligence; but at this age the like-lihood of death is the least.Earlier, we were infants and young children, and consequently more vulnerable; later, we shall undergo a progressive loss of our vigor and resistance which, though imperceptible (察觉不出的)at first, will finally become so steep that we can live no longer, however well we look after ourselves, and however well society, and our doctors; look after us. 46 .If we escape wars, accidents and diseases, we shall even-tually "die of old age", 47 .Some of us will die sooner, a few will live longer.But there

is a virtual limit on how long we can hope to remain alive, however lucky and robust we are.

Normal people tend to forget this process until they are reminded of it.We are so fa-miliar with the fact that man ages, that people have for years assumed that the process of losing vigor with time was something self-evident, like the cooling of a hot kettle or the wearing-out'of a pair of shoes.They have also assumed that all animals, and probably oth-er organisms such as trees, or even the universe itself, must in the nature of things "wear out".Most animals we commonly observe do in fact age as we do; 48 .But these are not analogous to what happens when man ages.A run-down watch is still a watch and can be rewound. 49 .But a watch could never repair itself it does not consist of living parts,only of metal, which wears away by friction (摩擦).We could, at one time, repair our-selves well enough, at least to overcome all but the most instantly fatal illnesses and acci-dents.Between twelve and eighty years we gradually lose this power; 50 .If we could stay as vigorous as we are at twelve, it would take about 700 years for half of us to die, and another 700 of the survivors to be reduced by half again.

A．Some old people are oppressed by the fear of death

B．an illness which at twelve would knock us over, at eighty can knock us out, and in-to our grave

C．and mechanical systems like a wound watch, or the sun, do in fact run out of energy

D．This decline in vigor with the passing of time is called ageing

E．And old watch, by contrast, becomes so worn and unreliable that it eventually is not worth mending

F．and this happens at a rate which differs little from person to person

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