问题 填空题

哺乳动物是高等生物,地球上大约有4000多种,除极个别的种类外,都具有______、______等特征.

答案

哺乳动物的主要特征体表有毛,牙齿分化,体腔内有膈,心脏四腔,用肺呼吸,大脑发达,体温恒定,胎生,哺乳.胎生哺乳是哺乳动物在生长发育方面最突出的特征.大大提高了后代的成活率.鸭嘴兽是卵生但是哺乳.因此除极个别的种类外,都具有胎生哺乳的特征.

故答案为:胎生;哺乳.

多项选择题
阅读理解

阅读理解。

     The world itself is becoming much smaller by using modern traffic and modern communication means.

Life today is much easier than it was hundreds of years ago, but it has brought new problems. One of the

biggest problems is pollution. To pollute means to make things dirty. Pollution comes in many ways. We

see it, smell it, drink it and even hear it.

     Man has been polluting the earth. The more people, the more pollution. Many years ago, the problem

was not so serious because there were not so many people. When the land was used up or the river was

dirty in one place, man moved to another place. But this is no longer true.

     Man is now slowly polluting the whole world.

     Air pollution is still the most serious. It's bad for all living things in the world, but it is not the only one

kind of pollution. Water pollution kills our fish and pollutes our drinking water. Noise pollution makes us

angry more easily.

     Many countries are making rules to fight pollution. They stop people from burning coal in houses and

factories in the city, and from putting dirty smoke into the air. Pollution by SO2 is now the most dangerous

kind of air pollution. It is caused by heavy traffic. We are sure that if there are fewer people driving, there

will be less air pollution.

     The earth is our home. We must take care of it. That means keeping the land, water and air clean. And

we must take care of the rise in pollution at the same time.

1. _____, our world is becoming much smaller.

A. Because of the rise in pollution

B. Thanks to science development

C. Because the earth is being polluted day and night

D. Because the earth is blown away by the wind every year

2. Hundreds of years ago, life was _____ it is today.

A. much easier than

B. as easy as

C. much harder than

D. as hard as

3. Pollution comes in many ways. We can even hear it. Here "it" means _____.

A. rubbish (垃圾)

B. noise pollution

C. air pollution

D. water pollution

4. Air pollution is the most serious kind of pollution because _____.

A. it makes much noise

B. it makes us angry more easily

C. it makes our rivers and lakes dirty

D. it's bad for all living things in the world

5. Which of the following is NOT true?

A. Many countries are making rules to fight pollution.

B. The pollution of the earth grows as fast as the world population does.

C. The problem of pollution is not so serious because there are not so many people living on the earth.

D. If people could go to work by bus or bike instead of car or motorbike, it would be helpful in fighting

    against the problem of SO2.