选择题：The pronoun “it” in the last but one paragraph refers to________·

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题目内容：

The pronoun “it” in the last but one paragraph refers to________·

A．crisis

B．stress

C．reaction

D．ill health

参考答案：【答案仅供学习，请勿对照自行用药等】

生态因子接近或超过某种生物的耐受极限而阻止其生存、生长、繁殖、扩散或分布时,这些因子称为______

生态因子接近或超过某种生物的耐受极限而阻止其生存、生长、繁殖、扩散或分布时，这些因子称为_________。

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演替按基质的性质可划分为____________和次生演替两类。

演替按基质的性质可划分为____________和次生演替两类。

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下列有关生物量的说法正确的是( )

下列有关生物量的说法正确的是( )A.陆地生态系统中最大的是热带雨林B.冻土带的生物量最低C.在水生生态系统中，水的最表层的生物量最大D.森林生态系统中，树冠的最顶部生物量最大

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Did it take him to get through the work?__________

Did it take him to get through the work?__________A．one and a half yearB．B two Scores of daysC．severa

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He taught himself to play the violin __________practising all night.

He taught himself to play the violin __________practising all night．A．byB．with byC．at byD．on

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