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阅读说明文《节能模范自天成》,回答问题。
        ①鸟在空中飞翔时既要克服地心的引力,又要战胜空气的阻力,消耗的能量是地面运动的十几倍。鸟在进化选择中发展了高效的节能结构和运动方式,成为人类空间动力学研究的模式动物。
        ②鸟类身体呈流线形,大大减少了在空气中运动时受到的阻力。鸟的胸部肌肉非常发达,而且积聚着大量的能量。飞行时,两只翅膀不断地上下扇动气流,产生巨大的下压抵抗力,足使鸟类能够快速前行。其次,鸟类的骨头是空心的,里面充有空气,头骨是一个完整的骨片,身体各部位的骨椎也相互愈合在一起,肋骨上有钩状突起,互相钩接,形成强固的胸廓。这些独特的骨骼结构不仅减轻了鸟的自身质量,还增强了飞翔的能力。
       ③鸟类的肺是实心的,呈海绵状,还连有9个气囊,在飞翔时,空气由鸟鼻孔吸入后,一部分在肺里直接进行气体交换,另一部分存入气囊,再经肺腔排出。所以,鸟类在飞行时只进行一次吸气,但肺部进行了两次气体交换,省了一半的呼吸耗能,保证了飞行中有足够的氧气供应。
       ④鸟类飞羽非常轻但结构坚韧。羽毛的中央是一根羽轴,两边着生羽片,羽毛基部还有一团绒羽。羽片是由许许多多平行细长的羽枝组成,每根羽枝可以看作一根小“羽毛”,两侧密生精细的羽小枝。这种天成的结构有效地减少了飞行时的空气阻力,展翅飞翔时能产生的升力,还能除震颤、消噪音。有些鸟在长途迁徒中,常排成行,利用头鸟振翅的气流,节省飞行用力。一只100克体重的鸟飞行1千米只消耗680焦耳的能量,只是陆地动物的1/3。
      ⑤鸟儿与空气动力学的结缘已有1亿年的历史,它们的节能结构和飞行原理,一直是人工航天器仿生的对象,但人类至今还没有弄清楚铭记珠扑翼原理,这也是人类一直造不出扑翼机的原因。

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    A drug that is used to treat serious bleeding could save thousands of lives of mothers giving birth. A world test of the drug found it reduced (降低) the risk of bleeding deaths during childbirth by nearly one third. The study included 20,000 women in 21 countries, mainly in Africa and Asia. The test was carried out by London School of Hygiene and Tropical Medicine. The drug is called tranexamic acid (凝血酸). It is low-cost and researchers said it does not cause serious side effects (副作用) for mothers or babies.

    The drug is used to treat mothers for serious bleeding during childbirth. Postpartum hemorrhage (产后出血) is the main cause of mothers' death around the world, according to the World Health Organization.

    Haleema Shakur is the project director for the test. She said though medical condition is improved in many countries, serious bleeding after childbirth remains a big problem in some parts of the world. “It's one of the biggest killers of mothers. In Africa and Asia, about 10% of women will end up with serious bleeding.” The drug works after a mother gives birth.

    Shakur said the best results were reported when the drug was given to women as soon as possible after childbirth. “The earlier you give it — within the first three hours after giving birth — the better the result is.”

    The next step will be to provide training for doctors and nurses on how to use it and then to find where the drug is needed. During the test, women were given the drug in a hospital. But researchers are looking for easier ways to use the drug so it can be more widely used in small clinics and the countryside.