题干

爆发于西非国家的埃博拉疫情已导致近2万人感染,死亡7588人,埃博拉病毒与动物细胞相比最主要的不同是( )

A:没有生命特征

B:没有蛋白质

C:没有细胞结构

D:没有遗传物质

上一题 下一题 0.0难度 选择题 更新时间:2018-07-11 09:48:49

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C

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    Xiaomi's sales strategy is largely responsible for the decline, having grown indistinguishable from that of many other Chinese manufacturers, according to Hong Kong-based cell-phone market journalist Yasuhiro Yamane. When the company first arrived on the scene in 2011 and 2012, its products were sold online by reservation only, building an air of exclusivity(排外)and lending the brand a high image. This strengthened the appeal of the smart phones, which resembled Apple's iPhones.

    But starting in 2013, Xiaomi began concentrating on high-volume sales, allowing many more resellers to carry its phones—a critical turning point in the company's fortunes. While sales increased, Xiaomi's products became viewed less as premium items and more as widely available, mass-market phones, according to Yamane.

    To keep consumers from losing interest, Xiaomi introduced a lower-end brand, Redmi, in July 2013. Phones in that family sell for 1000 yuan($150) or less, around half the price of products from the flagship Mi series.

    When China's economy began to skid at the end of 2014, the company leaned harder on the Redmi brand to hold on to market share in the following year—a grave mistake. Though it had some effect, the strategy ultimately “drove home the image of Xiaomi as a low-cost phone maker,” Yamane said.

    This should serve as a warning to other makers in China, where companies tend to emerge and quickly disappear due to their focus on short-term gains over long-term planning. “There is still a chance that Xiaomi could right itself and regain its old appeal,” Yamane said.

同类题5

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抗生素之殇
    ①1928年,英国微生物学家亚历山大·费莱明首次从青霉菌中发现了青霉素,从此人类进入了抗生素的黄金时代。第二次世界大战中,青霉素作为一线药用抗生素拯救了成千上万人的性命,价格曾一度比黄金还要昂贵。但在60多年后,很多抗生素失却了当年的雄风,成了医药学家的心头之痛。
    ②除了抗生素天然存在的毒副作用,抗生素耐药性问题是当今社会面临的重大问题之一。微生物适应环境的本领很强,当环境剧变时,它们不是束手待毙,而是用基因突变与环境抗争。生物与环境是统一的整体,成天生活在抗生素环境中的细菌,大部分不能存活,但总有漏网之鱼。侥幸存活的细菌在环境逼迫下会发生基因突变,一旦突变出抗药基因,就会绝处逢生。
    ③在大自然漫长的进化过程中,有“矛”就必有“盾”,抗生素固然是大自然产生的有效武器,但是大自然也必然保留着相应的破解方法。研究人员目前已经发现了数十类病原体具有耐受抗生素的抗性调控机制,这些病原体能够有效应对环境中出现的不同类型的抗生素。分裂生长速度越快的病原体,其耐药性产生的速度也就越快。
    ④据统计,人类使用抗生素之前和使用初期,世界范围内的耐药菌出现速度远慢于当今,随着不同种类抗生素的不断开发,临床上耐药菌开始呈指数级地出现。近年,多重耐药“超级细菌”的出现曾一度引起社会的恐慌,而目前新型抗生素的研发速度远慢于临床中耐药菌的产生速度。
    ⑤人们对于抗生素的滥用,正是在对耐药菌进行着无形的“人工筛选”。而如今世界范围内发达的交通运输使得这些人工筛选得到的耐药菌可以快速传播。即使你得了病坚持不用抗生素,体内确实没有筛选出大量的耐药菌,但是仍然有可能躺枪。
    ⑥虽然抗生素滥用的后果十分可怕,但是也不必杞人忧天和坐以待毙。首先,应该从每个人做起,不要感冒发烧后就自己给自己开药,应该遵循医嘱,科学合理用药。其次,应该呼吁医药和食品行业不要滥用抗生素,毫无节制地滥用抗生素无异于自掘坟墓。医药学家也正在与耐药菌赛跑,一方面改变药物的分子机构,以对付病原菌突变合成的酶;另一方面从世界各个生态环境中筛选新的抗生菌种。无论是赤日炎炎的热带,还是寒冷的极地;无论是大洋深处的喷口,还是地下的岩层,都有抗生素专家探求的目光。
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