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  3. Mark Twain once observed that giving up smoking is easy. He knew, because he’d done it hundreds of times himself. Giving up for

Mark Twain once observed that giving up smoking is easy. He knew, because he’d done it hundreds of times himself. Giving up for

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问题     Mark Twain once observed that giving up smoking is easy. He knew, because he’d done it hundreds of times himself. Giving up for ever is a trifle more difficult, apparently, and it is well known that it is much more difficult for some people than for others. Why is this so?
    Few doctors believe any longer that it is simply a question of will power. And for those people that continue to view addicts as merely "weak", recent genetic research may force a rethink. A study conducted by Jacqueline Vink, of the Free University of Amsterdam, used a database called the Netherlands Twin Register to analyse the smoking habits of twins. Her results suggest that an individual’s degree of nicotine dependence, and even the number of cigarettes he smokes per day, are strongly genetically influenced.
    The Netherlands Twin Register is a voluntary database that is prized by geneticists because they allow the comparison of identical twins (who share all their genes) with fraternal twins (who share half). In this case, however, Dr. Vink did not make use of that fact. For her, the database was merely a convenient repository of information. Instead of comparing identical and fraternal twins, she concentrated on the adult fraternal twins, most of whom had completed questionnaires about their habits, including smoking, and 536 of whom had given DNA samples to the register.
    The human genome is huge. It consists of billions of DNA "letters", some of which can be strung together to make sense (the genes), but many of which have either no function, or an unknown function. To follow what is going on, geneticists rely on markers they have identified within the genome. These are places where the genetic letters may vary between individuals. If a particular variant is routinely associated with a particular physical feature or a behaviour pattern, it suggests that a particular version of a nearby gene is influencing that feature or behaviour.
    Dr. Vink hopes that finding genes responsible for nicotine dependence will make it possible to identify the causes of such dependence. That will help to classify smokers better (some are social smokers while others are physically addicted) and thus enable "quitting" programmes to be customised.
    Results such as Dr. Vink’s must be interpreted with care. Association studies, as such projects are known, have a disturbing habit of disappearing, as it were, in a puff of smoke when someone tries to replicate them. But if Dr. Vink really has exposed a genetic link with addiction, then Mark Twain’s problem may eventually become a thing of the past.
选项 A、quitting smoking is no easy job.
B、kicking the habit of smoking demands a strong will.
C、some people are frustrated by failing to give up smoking.
D、some people may be destined to fail quitting smoking.
答案A
解析 本题问作者引用Mark Twain的例子是为了说明什么。第一段说Mark Twain说戒烟很容易，因为他自己就已戒过数百次了。这是幽默的说法，从反面说明戒烟不容易。作者引用Mark Twain的话引出戒烟难，从而进一步探讨有些人戒烟更难的原因。因此"戒烟不容易"为正确答案。戒烟需要很强的意志力：从第二段"Few doctors believe...a question of will power．And...to view addicts as merely ’weak’，recent genetic research may force a rethink"，可知意志力不是决定戒烟能否成功的原因和必要条件。作者通过否定一种观点来引出自己真正的观点：戒烟成功与否与基因有关。一些人为戒不了烟所困扰：第一段虽然也说到烟瘾不容易戒除，隐含人们对戒烟的苦恼，但作者举出例子不是为了说明戒烟的苦恼。有的人可能注定戒不了烟：首段提到马克.吐温的例子后，作者指出彻底根除烟瘾确实是有点儿困难。接着作者提到：众所周知，对有些人来说，戒烟要比其他人更难。这只是说戒烟难度很大，并且与基因有关。难高大并不代表注定戒不了烟，本项属于过度引申。
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