题干

某生物学家对一片森林中的林旅鼠和猫头鹰进行种群数量变化的调查研究,以便找出控制这些种群数量变化的因素。研究期间,由于林旅鼠患有一种由病毒引起的疾病而使种群数量下降。在正常情况下,森林中的猫头鹰是以林旅鼠为食,但当林旅鼠数量下降的时候,成年猫头鹰的数量(大约20只)仍能保持不变,新孵出的猫头鹰数量却大大下降。食物供应量的短缺导致了新生猫头鹰数量的减少,但没有减少成年猫头鹰的数量。对此,有人做出了如下解释,你认为正确的可能有
①蛋的孵化率下降 ②成年猫头鹰捕食能力比新生猫头鹰强
③营养不足使雌猫头鹰产蛋量减少 ④营养不良的新生猫头鹰更容易感染疾病而死亡

A:只有①③

B:只有②④

C:只有②③④

D:①②③④

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答案(点此获取答案解析)

D

同类题5

根据短文内容,用括号内所给动词的适当形式填空,必要时可加助动词或情态动词。

    Campbell Remess is a teenager from Australia. He has been sewing (缝制) teddy bears for sick children for several years.

    The story____ (begin) in 2013 when Campbell was nine years old. He told his parents that he wanted to give Christmas gifts to children in hospitals. But his parents said no, because with nine children of their own, buying presents for sick children would just cost too much. The little boy didn't give up, however. He decided____(make) their presents by himself.

    Campbell made his first teddy bear with his mother's sewing machine in his bedroom. It was hard for him as he had never done this before. He downloaded (下载) patterns from the Internet and learned how to make a teddy bear by____(watch) videos online. It took him five hours to finish his first teddy bear. He can now make a teddy bear in an hour. He has also started a project called “Project 365 by Campbell” in which he____(try) to make a teddy bear every day.

    Young Campbell uses his pocket money to buy materials for making teddy bears. To make more pocket money, he helps his parents with housework whenever he is free. Sometimes, he also sells his teddy bears online____(raise) money for sick children. Many people ____ (encourage) by Campbell's story and they give away free materials to him.

    Campbell____ (give) away about 1,300 teddy bears so far. He is now busy making this year's teddy bears. He said that he had never thought of stopping and he would keep putting smiles on people's faces.