Betting against an industry with addicts for customers carries obvious risks.【C1】______these are uncertain times for Big Tobacco. Electronic cigarettes, once dismissed as a novelty, now pose a serious【C2】______. E-cigarettes work by turning nicotine-filled liquid into vapour, which is then breathed in. A user is【C3】______said to be "vaping", not smoking. More important, he or she is not【C4】______all the toxic substances found in【C5】______smokes. In 2012 sales of e-cigarettes in America were between $300m and $500m, say analysts. That is【C6】______compared with the $80 billion-plus market for conventional cigarettes in the country. But e-cigarette sales doubled last year, and are expected to double again next year. Analysts believe sales of e-cigarettes could【C7】______sales of the normal sort within a decade. That may【C8】______how governments react. E-cigarettes are probably not good for you. One study showed that vaping【C9】______user"s lung capacity.【C10】______a switch from smoking【C11】______vaping could improve public health, some say. E-cigarettes may help smokers quit more【C12】______than nicotine patches or gum. This notion has not been thoroughly tested, however, so governments are【C13】______. America has warned e-cigarette manufacturers not to make health claims. New tobacco guidelines in Europe would either tightly limit the nicotine content of e-cigarettes or【C14】______them to undergo clinical trials. None of this has stopped companies from【C15】______to consumers. In America and Britain advertisements for e-cigarettes have appeared on television—forbidden【C16】______for standard cigarettes. Craig Weiss, the head of NJOY, America"s top-selling brand of e-cigarettes, swears to make traditional ones【C17】______. His ads crow: "Cigarettes, you"ve met your match." America"s tobacco giants do not think he is blowing smoke. Last year Lorillard (the maker of brands such as Newport and Kent) bought Blu, an e-cigarette maker. NJOY is rumoured to be facing a【C18】______, perhaps by Altria (the maker of Marlboro). Foreign cigarette makers also have【C19】______in the industry, while other firms are working on their own vaporous offerings. E-cigarette executives dream of beating traditional cigarettes. But as they struggle with taxes, patents and red tape, they may come to【C20】______Big Tobacco"s deep pockets.