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必修5 Unit 2（1） Unit 2 The United Kingdom 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 17,2017. 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. | 
