阅读理解。
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 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 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 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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1. The holly plant has 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 trees use ______.
A. chemical means
B. physical means
C. bitter chemicals
D. sandy materials
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.
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 Plant Leaves
