The branches could hardly _____ the weight of the fruit.

　　A. retain    B. maintain   C. sustain    D. remain

　  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 (保护) 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. 
【小题1】To defend themselves, oak trees use________.

A．chemical means	B．physical means
C．bitter chemicals	D．sandy materials

【小题2】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3】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

A desert is a beautiful land of silence and space. The sun shines, the wind blows, and time and space seem endless. Nothing is soft. The sand and rocks are hard, and many of the plants even have hard needles instead of leaves.

The size and location(分布) of the world’s deserts are always changing. Over millions of years, as climates change and mountains rise, new dry and wet areas develop. But within the last 100 yeas, deserts have been growing at a frightening speed. This is partly because of natural changes, but the greatest makers are humans.

Humans can make deserts, but humans can also prevent their growth. Algeria Mauritania is planting a similar wall around Nouakchott, the capital. Iran puts a thin covering of petroleum(石油) on sandy areas and plants trees. The oil keeps the water and small trees in the land, and men on motorcycles(摩托车) keep the sheep and goats away. The USSR and India are building long canals to bring water to desert areas.

In this passage, “needles” refers to _______.

A. small, thin pieces of steel.

B. long, thin pieces of branches.

C. small pointed growth on the stem(茎) of a plant.

D. small, thin pieces of sticks.

Which of the following is NOT true?

A. The greatest desert makers are humans.

B. There aren’t any living things in the deserts.

C. Deserts have been growing quickly.

D. The size of the deserts is always changing.

People in some countries are fighting a battle against _______.

A. the growth of deserts B. the disappearance of desert plants

C. natural changes  D. congenital climate

We can guess that Mauritania and Algeria belong to _______.

A. Asian countries 　　　　       B. American countries

C. European counties　　　 D. African countries

Choose the sentence which best gives the main idea of the passage.

A. The deserts of the world are always changing.

B. Man is to take measures to control the growth of the world’s deserts.

C. Deserts are lands of silence and space.

D. Deserts have grown at a fast pace in the past 10 years.