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下列关于二进制数的描述正确的是（ ）。
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你(David Brown)办公室的电脑是五年前购置的，最近经常死机。给你的上司Mr．Vance Ballard发个电子邮件，请他更新电脑， 以保证你办公室业务的正常运营。并祝他圣诞快乐。Words for reference：死机crash down；更新update
某种催化剂为铁的氧化物。化学兴趣小组在实验室对该催化剂中铁元素的价态进行探究：将适量稀硝酸加入少许样品中，加热溶解；取少许溶液，滴加KSCN溶液后出现红色。一位同学由此得出该催化剂中铁元素价态为+3的结论。 (1)请指出该结论是否合理并说明理由______。 (2)请完成对铁元素价态的探究： 限选实验仪器与试剂：烧杯、试管、玻璃棒、药匙、滴管、酒精灯、试管夹；3mol·L-1H2SO4、3% H2O2溶液、0.1mol·L-1KI、20%KSCN、蒸馏水。 ①提出合理假设 假设1：______； 假设2：______； 假设3：______。 ②设计实验方案证明你的假设 ③实验过程 根据②的实验方案，进行实验。请写出实验操作步骤、预期现象与结论。 实验操作 预期现象与结论 步骤1： 步骤2： 步骤3： ……
Labor Force The labor force is the part of a nation’’s population that works for pay or that is looking for a paying job. In 1800, the United States had about 2 million people in its labor force. Most of them worked on farms, most of whom were men. In 1993, about 130 million Americans were in the labor force. 96 million workers were found in large cities, 46 percent of whom were women. New Kinds of Jobs In the twentieth century, the U. S. labor force has undergone many changes. One of the most significant of these changes is in the decline in the number of blue collar jobs and the rise in the number of white-collar jobs. A blue-collar job involves manual or outdoor labor. Blue-collar workers include factory assemblers and welders; carpenters, plumbers(水暖工), mechanics, and painters; construction workers, and truck drivers. Although the number of blue-collar workers increased in the twentieth century, the future will see a declining need for such workers. Some of their jobs will be taken over by advanced automated and computerized machinery that can do certain blue-collar jobs more quickly and efficiently than people can. In contrast, a white-collar job involves work that is not chiefly manual. For example, white collar workers include accountants, engineers, teachers, lawyers, and sales personnel. In 1900, white collar workers made up about 20 percent of the labor force; today, 67 percent of all American wage earners hold white collar jobs. Advances in computer technology have created many new white-collar jobs, such as those in programming and information processing. These changes will continue to dramatically change the nature of existing jobs.The Rise of Women in the Labor Force Until 1940, the opportunities for women to hold jobs were limited. Prejudice and discrimination(歧视)against women forced many of them to find employment as teachers, nurses, and secretaries. In 1940, women held only 25 percent of the jobs. World War Ⅱ-1941 through 1945-brought about many changes in the labor force. Men were drafted to serve in the armed forces of the United States. At the same time, the country needed labor to keep factories running at full production to support the war effort. As a result, women were suddenly needed and hired even though they had been previously excluded from such jobs. Women not only repaired airplanes and land vehicles, but they also drove trucks, operated radios and ma chinery, and did clerical work. During the war years, the percentage of women in the labor force rose from 25 percent to 35 percent. Married women, many of whose husbands were in the armed forces, made up the greatest number of new women workers. In 1940, fewer than half of working women were single, but by 1945 a majority of women workers were married. By the end of the war, one out of every three workers in industry and business was a woman.The Postwar Years After the war, the men who returned from the armed forces went back to the same jobs they had held prior to the war. As a result, many women lost their wartime jobs. However, not all the women who had held jobs for the first time returned to their former roles as homemakers. Women had proved they could do these jobs well. As a result, the traditional barriers against the employment of women in such industries as steel and shipbuilding started to disappear. As the postwar prosperity continued, new positions became available for the returning men and for the many women workers now in the labor force. Many women found that they enjoyed not only employment outside their homes but also the benefits of paying jobs. Many women were beginning to see work as a permanent part of their lives. By earning their own income, they became less dependent and more self-sufficient. Their independence gave them new choices and made them aware of a wider range of roles available to them. The economic prosperity that followed the war also enabled many young couples to purchase houses. Many began raising families. Some women chose to stay at home to raise their children, while their husbands went to work. As a result, the percentage of women workers declined after the war, but it never went as low as it was in 1940.The 1960s to the 1990s The 1960s saw the beginning of many social changes in the United States, some of which were brought about by the women’’s liberation movement. Many women became keenly aware that they were often paid less than men for doing the same kind of work and that they were not promoted as easily or quickly as men. They also found that discrimination in jobs and in education still existed. As a result of women’’s protests, equal opportunity laws were passed that made discrimination against women in jobs and education illegal. This legislation opened up to women many business and professional positions that had previously been closed to them. The 1970s were troubled by ongoing inflation. For many couples, the high standard of living combined with the high cost of living, made it necessary for both the husband and wife to hold paying jobs. The two-income family became a way of life that continues today. Many divorced, separated, or widowed women also entered the labor force in the 1970s. The 1980s brought more changes. Many businesses were not able to survive the recession of that period. Many manufacturing industries, such as the auto, steel, textile, and clothing industries, suffered at the hands of increased competition from foreign countries. As a result, many plants and factories closed; the number of available jobs sharply declined. Because of the recession more mothers of young children entered the labor force. In general, families in the 1970s,’80s, and’90s have had fewer children than families of earlier generations. There has therefore been less need for women to stay at home for many years to care for young children, and more married women have been free to join the job market. Coupled with the trend toward two-income families, the labor force participation of married women with young children has risen dramatically since the 1970s. About 19 percent of mothers with children below age 6 were employed in 1970. In 1993, About 60 percent were employed.A Changing Labor Force Shifts from blue-collar to white-collar jobs and the increase in the number of working women continue to affect the labor force. These trends are altering the relationship between workers and their work, and people require new skills and training in all fields of employment. Nevertheless, today’’s (1990s) workers-whether blue-collar or white-collar, male or female-earn higher wages, work shorter hours, and receive more extra benefits than workers prior to the 1940s. In 1993, women held 46 percent of the paying jobs in the United States.
在PowerPoint中，要设置幻灯片的起始编号，应通过执行__________命令来实现。
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