题干

在一个生态系统中,食物链中的能量逐级减少最主要的原因是(     )

A:各级生物在进行生命活动时将一部分能量用于自身的新陈代谢

B:各类生物在摄取食物时,总有一部分不能被彻底消化

C:各类生物在捕食时有部分猎物会逃脱掉

D:各类生物在消化食物时总有一部分会被丢失掉

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答案(点此获取答案解析)

A

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    Tim Becker and his neighbors are doing something to make their neighborhood a safe area.

    When Tim Becker gets in his car to go shopping, he doesn't1 drive to a store and back home. He always looks 2up and down the streets of his neighborhood. He looks for anything 3 such as strange cars, loud noises, 4 windows, or people gathering on street corners.

    Tim 5 to a neighborhood watch group(巡逻小组)in Strongsville, Indiana, USA. The neighborhood watch group6 on his third Wednesday of every month. That's 7 Tim gets together with about ten of his neighbors to discuss community 8 Members of the neighborhood watch group want to help the police 9 their homes, streets, and families.

    Tina Stedman,10president of neighborhood watch group, agrees with Tim. “People seem to think that crime happens to other people but not 11them. Actually, it really happens,” she said, “and I think nobody has the12 to steal from other people or to make them feel 13 at their own homes.”

    Alex, a member of the group, said that all the neighbors were14to help one another, “We15 each other's homes. We keep watch on the neighborhood at night and on weekends. Usually a16 of four or five of us goes out together. If something doesn't look right, we will call the 17 For example, if we notice a group of teenagers who seem to be looking for 18 or someone destroying property(财产), we report to the police.”

    Alex feels the neighborhood watch group19a lot in reducing crimes. Her husband Jim agrees, “Police are good people, but they can't do20.