Many people use wood stoves and fireplaces to heat their homes．S

Many people use wood stoves and fireplaces to heat their homes．Scientists have become worried about the smoke that they give off．Harmful chemicals are in the smoke．The smoke is causing air pollution．The pieces of pollution,called soot,are floating in the air．They are too tiny to see．Scientists must use a microscope to see them. Small amounts of soot are safe,but large amounts can be dangerous．The govenment wants to limit this kind of pollution．It may stop people from using their fireplaces. The air is tested every day．When soot levels are high,more than 65 micrograms of soot per cubic meter,factories must stop making smoke．The government thinks that limit should be much lower. Factories produce the most smoke and soot．But the government thinks that all types of burning should be limited．The soot levels from factories and homes could be limited．Home owners may have to install new wood stoves that they comply with the new law．Or,they may not be able to bum on days when the air quality is bad. Residents of some towns are fined if they violate the burning ban．Scientists hope these new regulations will make the air cleaner and less harmful to breathe. Why is the air quality tested every day?
A、Just in case someone ask
B、Scientists like to take test
C、Scientists are not very bus
D、To keep track of pollution level
【正确答案】：D
【题目解析】：根据文章内容，我们可以找到关于“为什么空气质量每天都被测试”的线索。文章第三段明确提到：“The air is tested every day. When soot levels are high, more than 65 micrograms of soot per cubic meter, factories must stop making smoke.” 这表明空气质量测试是为了追踪污染水平。当烟尘水平超过每立方米65微克时，工厂必须停止排放烟雾。 选项A，“以防有人询问”，这在文章中并没有提及，也不是空气质量测试的原因。 选项B，“科学家喜欢测试”，这是一个主观的陈述，并不符合文章的实际内容。 选项C，“科学家不忙”，这同样是一个与文章内容不符的主观假设。 选项D，“为了追踪污染水平”，这直接回应了文章中的描述，即空气质量测试是为了跟踪烟尘等污染物的水平，以便在必要时采取行动限制排放。 因此，正确答案是D，即空气质量每天都被测试是为了追踪污染水平。