A、Current smokers exclusively. B、Second-hand smokers. C、With a lung problem. D、At age 40 or over. D根据文中who were healthy，at least

For years researchers have debated the whether smoking effects the lungs in men and women differently. In a most compelling study on the topic to date, researchers determined that women are twice as vulnerable to lung cancer as men. But in a surprising twist, they die at half the rate of men. The study, which was published last week in the Journal of the American Medical Association(J. A. M. A.), included 9,427 men and 7,498 women from throughout North America who were healthy, at least 40 years old and either current or former smokers. Over the course of more than eight years, a group of investigators led by Dr. Claudia Henschke of the Weill Medical College in New York City identified lung tumors in 113 of the men and 156 of the women. Then the researchers kept track of who lived and for how long, as well as the treatment participants were given. The study showed that both sexes tended to be in their late 60s when they received a lung-cancer diagnosis but that the women usually had smoked considerably less than the men. Still, at each stage of lung cancer, the women lived longer than the men. If the reported results are confirmed, there are a few hints from other research that might explain the sex difference. Women’ s bodies appear to have greater difficulty repairing the damage to their genes caused by smoking, but there is also some evidence that estrogen, which is found in women’ s lungs as well as their ovaries, may interfere with some tumors’ ability to grow. There is one thing about which all investigators are ready to agree; lung cancer is particularly deadly and almost entirely preventable. So the take-home message is clear: Don’ t smoke! If you do smoke, quit!
Questions
21. What is the talk mainly about?
22. What was one of the requirements for the participants of the study?
23. Over the course of more than eight years, how many of the participants developed lung cancer?
24. Which of the following is one finding of the study?
25. What is the consensus among all the investigators on smoking?