题干

下列化学实验操作,正确的是(    )

A: 点燃酒精灯  

B: 检查气密性     

C: 读取液体体积   

D: 加热液体

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答案(点此获取答案解析)

B

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                                                                                          森林医生——啄木鸟
      一个医生嘴巴尖,天天出诊到林间;
      敲敲听听多仔细,要动手术把头点。
      上面这个谜语猜一种动物,谜底是啄木鸟。可是起初我不但猜不中,而且人家揭了谜底后,我还不懂为什么把啄木鸟誉为“森林医生”。后来我随一支森林科学考察队去林区调查研究,通过一位生物学家对啄木鸟的介绍,和我自己对它的观察,我才真正认识到,“森林医生”这个称号,啄木鸟是当之无愧的。
      啄木鸟每天都起得很早,起身后第一件事就是给树木“检查身体”。它用嘴将一棵棵树从根到梢笃笃地轻轻敲打一通,听听有没有空声。经验告诉它,敲打时如发出空声,树干里面一定有虫,就立刻“动手术”。它的嘴长而直,末端尖锐,不但能啄破树皮和腐败的树干,而且能啄开坚硬的木质部;它的舌骨很发达,色围着头骨,舌骨起着特殊的弹簧作用,能使细长的舌条伸缩自如;舌面富含黏液,能把树中昆虫的幼虫和虫卵粘住;舌端生有向后倒长的小钩,能钩取树中较大的昆虫。它的鼻孔上覆盖着保护性的刚毛,可以防止碎木屑飞入鼻孔。值得一提的是,它的操作路线也很科学,工作时总是围绕着树干螺旋式地向上攀登,这样既可避免重复劳动,又不会有所遗漏。啄木鸟就凭着这套完备的“医疗器材”和独特的“医术”,专门捕食危害树木的昆虫,保护树木健康地成长。
      由于长期过着树栖生活,啄木鸟的翼变得既短又钝,不适于快飞和远翔,只能在林间通道或林中旷地作短距离滑翔,但是它的足趾却特别强劲有力,趾的排列也不像一般鸟类那样三趾向前,一趾向后,而变成二趾向前,二趾向后,而且具有锐利的钩爪,因此即使攀缘在笔直的树干上也不会滑落下来。此外,它的尾羽强韧坚直,羽轴特别粗硬,有弹性,可以当做支柱顶住身体,与两条岔开的腿形成一个“三足鼎立”之势,增加了悬立时的稳固性。

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    Singles' Day — the Chinese opposite of Valentine's Day has turned into a massive online shopping event. It is a day when single people are supposed to buy themselves presents. But there are sociological reasons behind China's “celebration” of single life. And the imbalance could have big consequences for the country.

    There were 34 million more men than women in China in 2011. Part of that is natural – usually there are 105 boys born for every 100 girls. But the Chinese gender ratio (性别比例) at birth is much more obvious. It was 116 boys to 100 girls in 2012. The one child policy is largely to blame. Brought in to limit population expansion, the policy allows only one child per family. But because male children are seen as more valuable, as well as more likely to support their parents in old age, some parents choose to have a son over a daughter. The result is that large numbers of men will likely never get married. In fact, one study has predicted that by 2030, 1 in 5 Chinese men in their 30s will never have married, while another states that 94% of unmarried people in China are men.

    Traditionally, China has seen high levels of marriage, usually among the young. Besides, the increased education and career opportunities for women have meant that marriages are happening later. It is also traditional that women often marry men of a higher socioeconomic status than themselves. So women at the top and men at the bottom find themselves alone. One study has even suggested a link between an imbalanced gender ratio and growth in violent crime in the country.

    Singles' Day can't solve all the problems China's singles face. Indeed, it is possible that it is causing even more problems, as men resort to(诉诸于) increasingly risky lines of work to increase their chances of gaining money and thus a wife. I am worried that as money starts to overcome romance, there is evidence that China's marriage market is increasingly materialistic.