说明文的阅读理解!(英语)

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. (NEMT2005江苏D篇)
69. To defend themselves, oak trees use________.
A. chemical means B. physical means
C. bitter chemicals D. sandy materials
70. 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.
71. 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
答案与解析：
69. B 植物保护自身方式判断题.由原文第三节首句Some plants, such as the oak tree, have thick and hard leaves that are difficult for animals to eat.体现答案.
70. C 植物保护自身方式判断题.由原文第四节This messenger sends to the roots the information to produce more nicotine可以推出答案.
71. B 标题判断题.认真阅读分析原文不难发现,原文第一节末句But plants can defend themselves by using both physical and chemical means.为主题句,全文围绕它展开说明,由此不难找到答案.