Animals can move from place to place, but plants cannot. When an animal is under attack, it can run away or fight back. Plants certainly cannot run away, and they lack teeth and claws. But plants can defend themselves by using both physical and chemical means.
Some plants have their own ways to keep animals away. For example, the leaves of the holly plant have sharp spines(刺) that discourage grass-eating animals. Holly leaves on lower branches have more spines than leaves on upper branches. This is because the lower leaves are easier for most animals to reach.
Some plants , such as the oak trees, have thick and hard leaves that are difficult for animals to eat. Some grasses may contain a sandy material; eating such grasses wears down the animal’s teeth.
Many plants also have chemical defenses. Some plants produce chemicals that taste bitter or cause an unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals. When a caterpillar(毛虫)bites a tobacco leaf, the leaf produces a chemical messenger. This messenger sends to the roots the information to produce more nicotine. The higher levels of nicotine discourage the caterpillar.
Many plants depends on both physical and chemical defenses. A certain plant in China , for instance, has prickly(多刺的) leaves, and each prickle contains poisonous venom(毒液). A single experience with this kind of plant will teach an animal to stay away from it in the future.
【小题1】The holly plant has more spines on the lower leaves because most animals .A．can get the lower leaves easily B．like eating the lower leavesC．like leaves with sharp spinesD．have teeth and claws【小题2】To defend themselves , oak trees use .A．chemical meansB．physical meansC．bitter chemicalsD．sandy materials【小题3】 How does tobacco protect itself against an attack from a caterpillar?A．Its leaves fight against the attack by physical means.B．Its roots send a messenger to discourage the caterpillar.C．Its roots increase the production of nicotine when it is attacked.D．Its leaves produce poisonous sand to drive the caterpillar away.【小题4】What would be the best title for this passage?A．Plants and AnimalsB．How Plants Defend ThemselvesC．Attacks and DefensesD．How Animals Eat Plant LeavesA
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(答案→)A
解析：试题分析:
【小题1】这是一道细节题。根据文章第二段the leaves of the holly plant have sharp spines(刺) that discourage grass-eating animals可知冬青的低枝多刺的原因是因为动物们要吃掉它们的枝叶，故选A。
【小题2】这是一道细节题。根据文章第三段的第一句Some plants , such as the oak trees, have thick and hard leaves that are difficult for animals to eat可知答案选B。
【小题3】这是一道细节题。根据文章第四段This messenger sends to the roots the information to produce more nicotine. The higher levels of nicotine discourage the caterpillar.可知答案选C。
【小题4】这是一道主旨大意题。文章第一段的最后一句是文章的主题句But plants can defend themselves by using both physical and chemical means.通过文章中所举事例可知文章论述的是植物保护自己的方法。