制作年代标尺是历史学习的有效方法之一，它能将复杂的历史较真观形象地展示出来.如图是一位同学在复习中国古代某一历史时期政权更迭时制作的年代标尺，其中①处应该是（　　）

配方x²﹣8x+____=（x﹣____）²．

根据短文理解，选择正确答案。

    Too much work and too much wine go together like biscuits and cheese, a new international studies finds. Employees who work more than 48 hours a week are 11 percent more likely to over-consume (过渡消费) alcohol than those who work standard time, Finnish researchers say. The study looked at more than 300,000 people in Australia, Europe and North America. No differences were seen between men and women, says the study, published in the British Medical Journal.

    Risky alcohol consumption is considered as more than 14 drinks a week for women and more than 21 drinks a week for men. About 20 percent of Australians drink at levels that put them at risk of lifetime harm from injury or disease. Drinking alcohol can affect the liver or cause brain damage, heart disease, high blood pressure and increase the risk of many cancers.

    Study author Marianna Virtanen said while alcohol might help ease the stress of working long periods of time, risky consumption could lead to difficulties in the workplace, such as poor performance. The European Union Working Time Directive ensures that workers in EU countries have the right to work no more than 48 hours a week, including overtime. “ But many people , for example well-educated managers and professionals, work much longer hours to achieve faster promotions (晋升), salary increases, and more control over work and employment,” said Prof. Virtanen from the Finnish Institute of Occupational Health.