Animals can move from place to place, but plants cannot. When an animal is under

   Animals can move from place toplace, but plants cannot. When an animal is under attack, it can run away orfight 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 theirown ways to keep animals away. For example, the leaves of the holly plant havesharp spines (刺) that discourage grass-eating animals. Holly leaves on lowerbranches have more spines than leaves on upper branches. This is because thelower leaves are easier for most animals to reach.

    Some plants, such as theoak tree, have thick and hard leaves that are difficult for animals to eat.Some grasses may contain a sandy material; eating such grasses wears down theanimal’s teeth.

    Many plants also havechemical defenses. Some plants produce chemicals that taste bitter or cause anunpleasant reaction. Some plants may fight against an attack by increasing theproduction of these chemicals. When a caterpillar (毛虫) bites a tobacco leaf,the leaf produces a chemical messenger. This messenger sends to the roots theinformation to produce more nicotine. The higher levels of nicotine discouragethe caterpillar.

    Many plants depend onboth 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 animalto stay away from it in the future.

1.The holly planthas more spines on the lower leaves 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

2.To defend themselves, oak treesuse________.

    A．chemical means B．physical means

    C．bitter chemicals                 D．sandy materials

3.How does tobacco protect itself against anattack from a caterpillar?

    A．Its leaves fight againstthe attack by physical means.

    B．Its roots send a messengerto discourage the caterpillar.

    C．Its roots increase the productionof nicotine when it is attacked.

    D．Its leaves producepoisonous sand to drive the caterpillar away.

4.What would be the best title for thispassage?

    A．Plants and Animals           B．How Plants Defend Themselves

    C．Attacks and Defenses      D．How Animals Eat Plant Leaves

试题答案

【答案】

1.D

2.B

3.C

4.B