Air pollution is a leading cause of cancer and classified among Group 1,or top, human carcinogens (致癌物质), said the International Agency for Research on Cancer (IARC), which is the World Health Organization's (WHO) cancer agency, on Oct 17,2013. The most widely used system for classifying carcinogens comes from the IARC, which places them into five groups. Group 1 carcinogens definitely cause cancer in humans. Group 2A is probably carcinogenic to humans, Group 2B is possibly carcinogenic, the carcinogenicity of Group 3 in humans is unclassifiable, and Group 4 is probably not carcinogenic to humans. Only a little more than 100 are classified as Group 1 cancer-causing substances, including ultraviolet radiation and tobacco smoke. “Our task was to evaluate the air everyone breathes rather than focus on specific air pollutants,” the lARC's Dana Loomis said in a statement. “The results from the reviewed studies point in the same direction: the risk of developing lung cancer is significantly increased in people exposed to air pollution.” In 2010, lung cancer resulting from air pollution killed 223,000 people worldwide, and there was also convincing evidence that it increases the risk of bladder (膀腕) cancer, according to the IARC. Air pollution is already known to raise risks for a wide range of illnesses, including respiratory and heart diseases. Air pollution is global, although the levels of it vary over space and time. Loomis said people in Asia, eastern North America, some places in Central America and Mexico, as well as North Africa have relatively high exposure. Developing countries with large populations and booming manufacturing sectors, such as China, are particularly at risk. Many cities in China, such as Beijing, frequently see smog. This week, Harbin, the capital city of Heilongjiang province, became the first Chinese city to officially suspend classes due to serious smog Many developed countries face similar problems, although to a lesser degree than most developing nations. In Europe, levels of many pollutants have fallen. But between 91 and 96 percent of Europeans living in cities are exposed to levels of PM2.5—tiny particles with a diameter of less than 2.5 micrometers—that are higher than the WHO safety limits, says a report published by the European Environment Agency on Oct 15. Although both the composition and levels of air pollution can vary dramatically from one location to the other, the 1ARC said its conclusions apply to all regions of the world. “Given the scale of the exposure affecting people worldwide, this report should send a strong signal to the international community to take action without further delay,” said Christopher Wild, director of the IARC. 小题1:What might be the best title of the passage? A．Signals of air pollution B．Safety limits of air pollution C．Air pollution, cancer risk D．Air pollution, smog risk 小题2:What’s the main task of IARC? A．To focus on cancer-causing substances. B．To evaluate the air quality. C．To study the developing risk of cancer. D．To send signals to the international community. 小题3:Why should the international community take action without further delay? A．The composition and levels of air pollution vary from place to place. B．More and more people in developing countries are exposed to air pollution. C．Developed countries face air pollution, the level of which is higher than the safety limits. D．A large number of people worldwide are exposed to air pollution.