单项选择题

We have to realise how old, how very old, we are. Nations are classified as "aged" when they have 7 per cent or more of their people aged 65 or above, and by about 1970 every one of the advanced countries had become like this. Of the really ancient societies, with over 13 per cent above 65, all are in Northwestern Europe. We know that we are getting even older, and that the nearer a society approximates to zero population growth, the older its population is likely to be-- at least, for any future that concerns us now. 　　To these now familiar facts a number of further facts may be added, some of them only recently recognised. There is the apparent paradox that the effective cause of the high proportion of the old is births rather than deaths. There is the economic principle that the dependency ratio-- the degree to which those who cannot earn depend for a living on those who can--is more advantageous in older societies like ours than in the younger societies of the developing world, because lots of dependent babies are more of a liability than numbers of the inactive aged. There is the appreciation of the historical truth that the aging of advanced societies has been a sudden change. 　　If "revolution" is a rapid resettlement of the social structure, and if the age composition of the society counts as a very important aspect of that social structure, then there has been a social revolution in European and particularly Western European society within the lifetime of everyone over 50. Taken together, these things have implications which are only beginning to be acknowledged. These facts and circumstances had a leading position at a world gathering about aging as a challenge to science and to policy, held at Vichy in France. 　　There is often resistance to the idea that it is because the birth rate fell earlier in Western and Northwestern Europe than elsewhere, rather than because of any change in the death rate, that we have grown so old. Long life is altering our society, of course, but in experiential terms. We have among us a very much greater experience of continued living than any society that has ever preceded us anywhere, and this will continue. But too much of that lengthened experience, even in the wealthy West, will be experience of poverty and neglect, unless we do something about it. 　　If you are in your thirties, you ought to be aware that you can expect to live nearly one third of the rest of your life after the age of 60. The older you are now, of course, the greater this proportion will be, and greater still if you are a woman. According to the text, really aged societies may include