两台气化炉运行时，当高压氮气压力低于氧气总管压力应如何处理？
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直线l：y＝x－1被圆(x－3)2＋y2＝4截得的弦长为 ．
D
Among rich countries, people in the United States work the longest hours. They work much longer than in Europe. This difference is quite surprising because productivity per hour worked is the same in the United States as it is in France, Spain and Germany, and it is growing at a similar speed.
In most countries and at most times in history, as people have become richer they have chosen to work less. In other words they have decided to "spend" a part of their extra income on a fuller personal life. Over the last fifty years Europeans have continued this pattern, and hours of work have fallen sharply. But not in the United States. We do not fully know why this is. One reason may be greatly lower taxes in America, which increase the rewards to work. Another may be more satisfying work, or less satisfying personal lives.
Longer hours do of course increase the GDP (国内生产总值). So the United States has produced more per worker than, say, France. The United States also has more of its people at work, while in France many more mothers and older workers have decided to stay at home. The overall result is that American GDP per head is 40% higher than in France, even though productivity per hour worked is the same.
It is not clear which of the two situations is better. As we have seen, work has to be compared with other values like family life, which often get lost in its interest. It is too early to explain the different trends (趋势）in happiness over time in different countries. But it is a disappointing idea that in the United States happiness has made no progress since 1975, while it has risen in Europe. Could this have anything to do with trends in the work-life balance ?
51. From the text we know that the author __________.
A. believes that longer working hours is better
B. prefers shorter working hours to longer ones
C. says nothing certain about which pattern is better
D. thinks neither of the patterns is good
52. Which of the following countries has more of its people at work?
A. Spain. B. France. C. Germany. D. America.
53. In the last paragraph, the underlined word "which" refers to_________.
A. family life B. situations C. other values D. trends
54. What message can we get from the text?
A. The GDP of Europe, is higher than that of America.
B. Two possible reasons are given for working longer hours in the US.
C. People all over the world choose to work less when they are richer.
D. Americans are happier than Europeans.
55. Which of the following would be the best title for the text?
A. Americans and Europeans. B. Staying at Home.
C. Work and Productivity. D. Work and Happiness.
皮带机的减速机在运转时轴承温度不应低于65℃。（）
患者，23岁，有国外旅游史，一天前出现腹部隐痛不适，排大便35次，每次量均较多，先为水样便，再转为洗肉水样大便，呕吐水样物10次，不伴恶心，无发热，无里急后重。体查：声音轻度嘶哑，眼窝明显下陷，皮肤褶皱恢复较慢。根据题意，回答下 * * 题。
第一天的补液量应是（）
A.1000~2000ml
B.4000~8000ml
C.8000~10000ml
D.2000~3000ml
E.12000ml以上
健美操的艺术性主要体现在“健、力、美”的项目特征上。