which directs gene expression. According to the researchers, methylation happened in genes linked to smoking­related diseases.

　　 In all, about one­third of known genes in smokers were found affected. While most of these genes went back to normal levels five years after a person quit, changes in 19 genes - including the TIAM2 gene, which is linked to lymphoma - lasted 30 years, NBC reported.

　　 "The encouraging news is that once you stop smoking, most of DNA methylation signals return to never­smoker levels after five years, which means your body is trying to cure itself of the harmful impacts of tobacco smoking，" Joehanese said.

　　 Cigarette smoking is the leading preventable cause of death in the U．S., according to the Centers for Disease Control and Prevention. Each year, more than 480,000 people die from its health effects. That figure is equal to nearly one in five deaths overall.

　　 So if you're a smoker, seriously consider quitting for the sake of your health; if you're a non­smoker, never try your first cigarette.

　　【文章大意】　 本文为说明文，题材为环保健康类。吸烟不仅是多种疾病的诱因，研究发现它还会对DNA造成长远的不利影响。

　　1. What's the new finding of the study?

　　A．Smoking can contribute to various diseases.

　　B．It won't work even if smokers quit smoking.

　　C．Smoking causes nearly one in five deaths overall.

　　D．Smoking causes long­term damage to your DNA.

　　解析：D　细节理解题。根据第一段的A new study has found that cigarette smoking leads to disease­causing DNA damage that can last more than 30 years after a person quits可知，这个研究主要表明吸烟会对DNA造成长期不良影响。

　　2. What does the underlined word "hazardous" in Paragraph 2 mean?

　　A．Common. B．Dangerous.

　　C．Indirect. D．Temporary.

解析：B　词义猜测题。根据划线词后面的include an increased risk for diseases like cancers, as well as lung and cardiovascular disorders可知，这里是