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肛门外括约肌（）。
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One of the greatest economic and social changes of the post-war years has gone largely unnoticed. It is that more and more women are going out to work. Today in the United States, in Japan and in the United Kingdom, almost 40 per cent of the work force is female. 16. ______ Most women now work far longer hours than men -in factory, shop or office as well as in the home as cook, cleaner, child rearer, shopper and home-maker. This "double burden" means that the average woman who goes out to work is now putting in an 80-hour working week -twice as long as most men. So equality depends not only on women sharing in paid employment but also on men sharing in the tasks of the home. At the moment husbands in all industrialised countries contribute very little to domestic work and recent research shows that this contribution does not increase when the wife goes out to work. American researcher Joan Vanek, for example, found that the average father in the United States spends only 12 minutes a day with his children. Overall, women’s unpaid work in the U.S.A. is estimated at about 40 per cent of the Gross Domestic Product. 17. ______ The reasons why women earn less than men go deeper than legislation. And again the main cause is the double burden’ of home responsibilities which means that many women have to take part-time jobs, or less demanding jobs, and that they have less time for training and less opportunity for promotion. As children, girls are educated and conditioned either for no employment at all or for more manial and lower-paid jobs. As workers, they are crowded into industries like textiles, food, clothing, retailing -where they compete with each other for low-paid and insecure jobs which require little skill or training and offer little chance of promotion. A recent survey in Sweden shows that women have a choice of about 25 different occupations whereas a man chooses from over 306 careers. Indeed certain countries, says the OECD, "have come to rely on a supply of female labour which costs little and enjoys little protection". 18. ______ Single parent families are increasing in almost every industrialised country. In Britain at least 600,000 families are now headed by single mothers and the number is growing by 6 per cent a year. The main cause is the rise in divorce rates which have doubled in many countries during the last 15 years. 19. ______ As the ILO notes, pensioners are the poorest social group in the industrialised world. But here too it is the women who are worst off -partly because they tend to live longer than men and partly because inequality during their working lives is reflected in reduced pensions. In the United States, for example, the 8 million women who are over the age of 65 make up by far the poorest group of people in America -with almost half of them living below the official poverty line. 20. ______ The first half of the U.N. Decade for Women has now gone and the vast majority of women in the industrialised countries have seen little or no benefit. Equal-pay legislation in almost all industrialised countries has been one of the big achievements of these five years. The task for the next five years is to achieve equal work which will give substance to equal pay. The biggest barrier is that working women now do two jobs. And overcoming that barrier is as much of a challenge to men as it is to women.A. But even in the work-place itself, women’s wages are everywhere lower than men’s. In the U.K., women are paid an average of 25 per cent less. In the U.S.A., they are paid 40 per cent less. And this is despite equal pay legislation in most industrialised countries.B. The result of this inequality is that women have more than their fair share of poverty. And particularly hard-hit are the families dependent on a woman’s earnings.C. In theory this should mean that women are becoming better-off, liberated, equal. But in practice it is a different story.D. For women at work, the final irony is that the trade unions -which have done so much to improve the pay, conditions and benefits of work forces in the industrialised world -are also dominated by men. In America’s garment industry, 80 per cent of the union members are women but 21 of the 22-member board of the union are men. In New Zealand only 15 of the country’s 323 unions have any women executives despite the fact that women carry over a third of all union membership cards.E. It is these single-parent families, says the International Labour Organisation, which make up the fastest rising group in any classification of the poor population. Even after the receipt of benefits, the incidence of poverty is only just below that of pensioners and is much higher than in any other group.F. In the case of younger women, such work loads are commonly combined with frequent pregnancy, childbirth and breast-feeding I exhausting processes for any woman’s body, but particularly debilitating when compounded by inadequate food and long hours of back-breaking work in the fields.
细菌在血中大量繁殖是（）。
Koalas, an Australian tree-climbing animal, are very particular about what they eat, devoting themselves entirely to a diet of the leaves of eucalyptus trees. But there are problems associated with an exclusive diet of leaves, especially if, like the koala, you happen to be a relatively small animal. One of these problems is that the leaves of trees are rich in fibre, and so resist digestion. Eucalyptus leaves are worse than most, for they contain large amounts of lignin, the indigestible, woody material found in the cell walls of many plants. But there is another drawback for the koala. The ratio of an animal’s gut volume to its energy requirements depends on body mass; the smaller it is, the lower the ratio. So tiny leaf-eaters are likely to have difficulty processing sufficient quantities of their poor-quality food to meet their metabolic needs. S. J. Cork and T. J. Dawson of the University of New South Wales and I. D. Hume of the University of New England have made a study of the koala’s digestion. They have identified three major factors that allow koalas to exploit its fibre-laden diet. In the first place, the koala has a discerning digestive system; like the rabbit, it can regulate the passage of food through its gut in a way that discriminates between particles of different sizes. The alimentary canal retains and solutes smaller, more digestible particles, while expelling unwanted, coarser matter. This is probably a space-saving exercise; it has the effect of increasing the rate at which raw material can be fed into the system. The second factor behind the koala’s success is that it has a low overall requirement for metabolic energy, compared to other Australian animals of similar size. So it saves on its fuel needs. In this respect, the koala is not dissimilar to another slow-moving, leaf eating mammal, the three-toed sloth. Thirdly, eucalyptus leaves have hidden qualities. Despite the large quantity of lignin, such leaves are rich in digestible energy -especially in the form of fatty substances. Not all such resources are available to the koala’s metabolic machinery; essential oils are passed out, for example. But some fatty substances are available, as are sugar and starch. It is these compounds that satisfy the bulk of the koala’s energy needs. Surprisingly, constituents of the eucalyptus’s cell walls, such as cellulose, are less important. Some cellulose is digested, but the koala’s accomplishments in this field do not rival those of other animals that reshow. The purpose of Cork, Dawson and Hume study is to
钠石灰中含（）
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