A
New research has found that even if you give up smoking, the damage it has done to your genes (基因) will stay there for a much longer time.
In the research, a team of US scientists studied the blood of 16, 000 people. Among them, some were smokers, some used to smoke, and the rest were nonsmokers. Scientists compared their genes and found that more than 7, 000 genes of those smokers had changed—a number that is onethird of known human genes.
According to NBC News, both heart disease and cancer are caused by genetic changes. Some people may have had the changes when they were born, but most people get them in their daytoday lives while doing things like smoking.
When you stop smoking, a lot of these genes will return to normal within five years. This means your body is trying to heal (治愈) itself of the harmful effects of smoking. But the changes in some of the genes stay for longer. They can stay for as long as 30 years. It's almost like leaving a footprint on wet cement (水泥) —it will always be there, even when you've walked away and when the cement becomes dry.
Although the study results may make people unhappy, there is a bright side：the findings could help scientists invent medicine to treat genetic damage caused by smoking or find ways to tell which people have heart disease or cancer risks.
语篇大意：这是一篇说明文。研究发现即使已经戒烟，它对基因造成的伤害还会保留很长的时间，基因变化会使人患心脏病和癌症。
21. The function of Paragraph 1 is to ________.
A．give an example
B．arouse readers' interest
C．make an argument
D．give the main idea of the passage
答案：B
解析：推理判断题。由第一段新的研究发现，即使你戒烟，它对你的基因造成的损害也会在身体里停留更长的时间以及下文通过实验说明这一问题和具体的影响可知，第一段点明了短文的主题，同时第一段的作用也是引起读者的兴趣。故B选项正确。
22. Most genetic changes happen because of ________.
A．people's condition at birth
B．environmental pollution
C．people's bad living habits
D．heart disease and cancer
答案：C
解析：细节理解题。由第三段“Some people may have had the changes when they were born, but most people get them in their daytoday lives while doing things like smoking.”可知，有些人可能在出生时基因就已经发生了变化，但大多数人的基因变化是日常生活中的不良习惯如吸烟所导致的。故C选项正确。
23. Which of the following statements is true?
A．The findings are the fruit of more than three years' research.
B．The findings have prevented more people from starting smoking.
C．The findings offer evidence that a damaged gene can heal itself.
D．The findings help to find cures for genetic damage caused by smoking.
答案：D
解析：细节理解题。由最后一段“the findings could help scientists invent medicine to treat genetic damage caused by smoking or find ways to tell which people have heart disease or cancer risks.”可知，这项发现可以帮助科学家发明药物来治疗吸烟造成的基因损伤，或者找到方法来判断哪些人有患心脏病或癌症的风险。所以D选项“这些发现有助于找到治疗吸烟引起的基因损伤的方法”是正确的。
