A.between B.imitate C.accelerate D.otherwise Phrases: A.enabling the bird to【T13】______ B.it【T14】______could C.would be di

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问题 A.between   B.imitate   C.accelerate   D.otherwise Phrases:
A.enabling the bird to【T13】______
B.it【T14】______could
C.would be difficult to【T15】______
D.from【T16】______its feathers
    The emperor penguin traps air in its feathers. Not only does this insulate the bird against extreme cold but it also enables it to move two or three times faster than【T17】______. How? Marine biologists have suggested that it does so by releasing tiny air bubbles【T18】______. As these bubbles are released, they reduce friction on the surface of the penguin’s wings,【T19】______.
    Interestingly, engineers have been studying ways to make ships go faster by using bubbles to reduce friction against their hulls (船身).However, researchers acknowledge that further investigation is challenging because "the complexity of penguin’s wings【T20】______.
【T20】

选项

答案C

解析 空格前because引导从句,从句主语为the complexity,要想保持句子结构完整,此处需要填入谓语动词,因此C选项正确。通过语义也可以解题:研究者们认为进一步的研究是个挑战,因为企鹅王翅膀的复杂性是很难模仿的,C选项填入后语义通顺。                                                                                 
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