一根长为l的易断的均匀细绳的两端分别固定在天花板上，如图所示。今在C处挂一砝码，下列

2010年夏天，罕见的高温袭击北半球，从北美到亚洲，都经历了有气象记录以来最热的夏天。但气象专家警告说，入冬后欧洲可能将面临“千年极寒”，中国等亚洲地区也可能难以幸免。这种异常气候与干扰大洋暖流活动的“拉尼娜”现象有关。这表明[ ]

①气候的变化和发展遵循其固有的规律

②气候变化尽管复杂，但其规律性可以被认识

③科学技术的发展使人们完全掌握了气候规律

④气候规律是否发挥作用与科技水平密切相关

A、①②

B、③④

C、①③

D、②④

按规定，一般每个受伤人员休息在1个工作日以上，( )个工作日以下。

A．30

B．60

C．90

D．105

男性，68岁，食管癌，食管明显梗阻的病人，术前减轻食管黏膜水肿的措施是

A．术前禁食
B．营养支持
C．纠正水、电解质、酸碱失衡
D．加强口腔卫生
E．术前3天温盐水洗胃

On the first Earth Day, the U.S. was a poisoned nation. Dense air pollution blanketed cities like Los Angeles, where smog alerts were a fact of life. Dangerous pesticides like DDT were still in use, and water pollution was rampant—symbolized by raging fires on Cleveland’s Cuyahoga River. But the green movement that was energized by Earth Day— and the landmark federal actions that followed it—changed much of that. Today air pollution is down significantly in most urban areas, the water is cleaner, and even the Cuyahoga is home to fish again.

But if the land is healing, Americans may be sickening. Since World War Ⅱ, production of industrial chemicals has risen rapidly, and the U.S. generates or imports some 19 billion kg of them per day. These aren’t the sorts of chemicals that come to mind when we picture pollution—huge plants spilling contaminated wastewater into rivers. Rather, they’re the molecules that make good on the old "better living through chemistry" promise, appearing in items like unbreakable baby bottles and big-screen TVs. Those chemicals have a, habit of finding their way out of everyday products and into the environment—and ultimately into living organisms. A recent biomonitoring survey found traces of 212 environmental chemicals in Americans—including toxic metals, pesticides, etc. "It’s not the environment that’s contaminated so much," says the director of the Cincinnati Children’s Environmental Health Center. "It’s us."

As scientists get better at detecting the chemicals in our bodies, they’re discovering that even tiny quantities of toxins can have a potentially serious impact on our health—and our children’s future. Chemicals like bisphenol A (BPA) and phthalates—key ingredients in modern plastics—may disrupt the delicate endocrine system. A host of modern ills that have been rising unchecked for a generation—obesity, diabetes, attention-deficit disorder —could have chemical connections. "We don’t give environmental exposure the attention it deserves," says Dr. Philip Landrigan. "But there’s an emerging understanding that kids are uniquely susceptible to environmental hazards."

Washington has been slow to arrive at that conclusion. The Toxic Substances Control Act (TSCA), the 34-year-old vehicle for federal chemical regulation, has generally been a failure. The burden of proving chemicals dangerous falls almost entirely on the government. And the Environmental Protection Agency (EPA) has been able to issue restrictions on only a handful of chemicals and has lacked the power to ban even some dangerous cancer-causing substances.

But change is coming. The Obama Administration is taking a closer look at chemicals. More important, Congress may finally be ready to act. "We can’t permit this assault on our children’s health—and our own health—to continue," says Senator Frank Lautenberg.

The environmental chemicals in the U.S（）

A. come from spilling contaminated wastewater

B. appear in everyday products

C. cause more contamination to the environment

D. have few sorts but serious impact

打开工作簿文件EXC.XLS，对工作表“选修课程成绩单”内的数据清单的内容进行自动筛选(自定义)，条件为“成绩大于或等于80并且小于或等于90”，筛选后的工作表还保存在：EXC.XLS工作簿文件中，工作表名不变。