第17题: [单项选择]A. The number of smokers has been falling about 2 percent a year. B. The number of smokers has been rising 20 percent a year. C. The number of smokers has been rising 2 percent a year. D. The number of smokers has been falling 20 percent a year. 参考答案:C 答案解析:[听力原文] What is the recent important development observed in developing countries