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Despite their varied designs, navigation computers used in cars ______.
Mr. Smith is in good health now for it is quite a long time since he ______.
Text 1Mark 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 soFew 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. The author cites the example of Mark Twain to show that（）
Text 2When enthusiasts talk of sustainable development, the eyes of most people glaze over. There is a whiff of sack-cloth and ashes about their arguments, which usually depend on people giving up the comforts of a modern economy to achieve some debatable greater good. Yet there is a serious point at issue. Modern industry pollutes, and it also seems to cause significant changes to the climate. What is needed is an industry that delivers the benefits without the costs. And the glimmerings of just such an industry can now be discerned.That industry is based on biotechnology. At the moment, biotech’s main uses are in medicine and agriculture. But its biggest long-term impact may be industrial. Here, it will diminish demand for oil by taking the cheapest raw materials imaginable, carbon dioxide and water, and using them to make fuel and plastics.Plastics and fuels made in this way would have several advantages. They could accurately be called "renewables", since nothing is depleted to make them. They would be part of the natural carbon cycle, borrowing that element from the atmosphere for a few months, and returning it when they were burned or dumped. That means they could not possibly contribute to global warming. And they would be environmentally friendly in other ways. Bioplastics are biodegradable, since bacteria understand their chemistry and can therefore digest them. Biofuels, while not quite "zero emission" from the exhaust pipe (though a lot cleaner than petrol and diesel), would be cleaner overall even than the fuel-cell technology now being touted as an alternative to the internal-combustion engine. That is because making the hydrogen that fuel cells use is not an environmentally friendly process, and never will be—un less it, too, uses biotechnology.All this will, in the end, depend on costs. But these do not look unfavourable. Already, the price of bioplastics overlaps the top end of the petroleum-based plastics market. Bulk production should bring prices ’down, particularly when the raw materials are free. Meanwhile, ethanol would be a lot easier to introduce than fuel cells. Existing engines will run on it with minor tweaking, so there is no need to change the way ears am made. And since, unlike hydrogen, it is a liquid, the fuel-distribution infrastructure would not need radical change.The future could be green in ways that traditional environmentalists had not expected. Whether they will embrace that possibility, or stick to sack-cloth, remains to be seen. One advantage of the biofuels is that（）
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