For decades the market for expensive headphones was mainly limited to hi-fi fans. But【C1】______the boxy stereo system in the corner of the bedroom is largely a thing of the past, and young music fans listen【C2】______on portable devices, headphones have become as much of a fashion statement as the music player itself.【C3】______the first to spot the potential of this market was Dr Dre and Jimmy Iovine. In 2008 they【C4】______their Beats range of headphones, to great【C5】______. They have all but created a new product【C6】______: premium-priced headphones whose sound quality is good enough,【C7】______which mainly sell on their brand image. Beats Electronics and its founders have proved skilled【C8】______using celebrity endorsements and product placement to【C9】______his headphones. In America the company now has almost half the market for premium-priced headphones, compared with 21% for Bose, a longer-established maker. Beats headphones are exactly what hip-hop fans want, but might not suit opera lovers. Overall,【C10】______, they are a lot better than the earphones that come free with most portable devices. There is in any case a limit to how good music will sound through even the best headphones. Most of the music tracks on portable music players are in the form of mp3 audio files, in which the music has been【C11】______to make the files smaller and【C12】______fit more of them into a【C13】______amount of storage capacity. Since consumers have been persuaded, largely by Beats, that it is worth paying a high price for headphones, perhaps they could be persuaded to turn their backs on cheap mp3s and【C14】______recordings in true high fidelity. If sales of hi-fi recordings take off it may【C15】______the market for really top-class headphones like those of Grado Labs, another American firm. Grado has for decades relied on reviews in specialist magazines, and word-of-mouth【C16】______from fans, to spread news of its headphones'【C17】______reproduction. In contrast to Beats, it has avoided imagemaking it has not【C18】______since 1964 Unlike Dr Dre, then, its【C19】______are less tied to the【C20】______tastes and fast-changing fashions of the young.
【答案解析】解析：空格所在的主句是条件从句If sales of hi-fi recordings take off可能导致的结果。如果高保真音乐的销量飞涨(take off)，顶级耳机的市场(the market for really top-class head-phones)就会得到提振。故A项boost“提高，促进”符合语义要求。