Air pollution is a growing problem throughout the world. Indoor air pollution is (41) .............. of the leading causes of lung cancers. Families in developing countries use open stoves for cooking and heating (42) .............. homes. These homes do not have proper ventilation. The smoke, which is (43) ............... of chemicals and carcinogens, gets trapped inside where families eat and sleep. Outdoor pollution also (44) .............. disease and illness, especially in industrial cities such as Beijing, China, where cancer is (45) ............ leading cause of death. China relies heavily on coal, which is considered the dirtiest (46) .............. of energy. According to the European Union, only one percent of urban dwellers in China (47) ................ clean air on an average day. Neighboring countries including Japan and Korea receive much of Chinas pollution in the (48) ............. of acid rain. This pollution results mainly from the coal powdered factories, which produce in expensive goods (49) ........... North American and European consumers. Outdoor air pollution is also a concern in many wealthy countries. Those who live and (50) ............ in urban centres such as Los Angeles or Toronto experience many warm days beneath a layer of smog.