楼梯已计算建筑面积的（），不再计算建筑面积。A.其下方空间不论是否利用 B.其下方空

由于钢轨受车轮压力会产生挠曲，为抵抗挠曲，钢轨应有可（）。

该患者的诊断应首先考虑

A．躖外翻伴躖囊炎

B．躖趾跖趾关节处急性炎症

C．痛风性关节炎

D．松毛虫性关节炎

E．类风湿关节炎

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.

According to Senator Frank Lautenberg, （）

A. actions should be taken to protect children from the environmental chemicals

B. more people begin to realize children’s susceptibility to environmental hazards

C. we should give more attention to environmental exposure

D. it’s more important and urgent to protect children’s health

变压器的寿命是由绝缘（）材料的（）程度决定的.而绝缘材料的老化，主要取决于运行温度、绝缘材料结构中的氧气含量、含潮率等。

航空燃气涡轮发动机中常用的燃烧室结构型式有（）三种.

A.管型、环型和管环型

B.等外径、等内径和等中径

C.鼓型、盘型和鼓盘型

D.扩张型、收敛型和直筒型