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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 grasseating animals.Holly 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 tree, have thick and hard leaves that are difficult for animals to eat.Some grass may contain a sandy material；eating such grass wears down the animals' 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 the roots the information to produce more nicotine.The higher levels of nicotine discourage the caterpillar.
Many plants depend 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.
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语篇解读：本文是一篇说明文。文章介绍了不能移动的植物是如何保护自己的，有些植物采取了物理方法，有些采取了化学方法。
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1．The leaves of the holly plant have more spines on the lower branches because most animals________.
A．are not tall enough
B．like the lower leaves only
C．are not clever enough
D．can get the lower leaves easily
解析：选D 细节理解题。根据文章第二段中的This is because the lower leaves are easier for most animals to reach.可知，冬青树底部叶子上的刺比上部多的原因是动物更容易够到底部的叶子。
2．To defend themselves, oak trees use ________.
A．chemical means B．physical means
C．bitter chemicals D．sandy materials
解析：选B 细节理解题。根据第三段中的Some plants, such as the oak tree, have thick and hard leaves that are difficult for animals to eat.可知，橡树的叶子又厚又硬，很难被动物吃掉。所以橡树使用的是物理方法来保护自己。故B项正确。
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.
解析：选C 细节理解题。根据第四段中的When a caterpillar (毛虫) bites a tobacco leaf, the leaf produces a chemical messenger.This messenger sends the roots the information to produce more nicotine.The higher levels of nicotine discourage the caterpillar.可知，当毛毛虫叮咬烟叶时，烟叶会产生一种化学信使，这个信使会把信息传送到树根以分泌出更多的尼古丁来驱赶毛毛虫。
4．What would be the best title for this passage?
A．Plants and Animals
B．How Plants Defend Themselves
C．Attacks and Defenses
D．How Animals Eat Plants' Leaves
解析：选B 标题归纳题。本文主要讲述了不能移动的植物是如何保护自己的，有些植物采取了物理方法，有些采取了化学方法。
