2.The scientists are interested in studying tree rings because tree rings can tell ______.

　A.whether a tree was strong or not B. whether people took good care of the trees or not

　C. whether the climate was good or not D. how old the trees were

1._____ in good climate.

　A. Tree rings grow far from each other B. Tree rings become thinner

　C. Trees don’t need sunshine or rainfall D. People can cut down most of the trees

5.Halley’s Comets came back _____.

　A. in 1990 B. in 1980 C. in 1986 D. in 1989

　Passage 3

　Do you know something about tree rings (年轮)? Do you know they can tell us what the weather was like, sometimes even hundreds of years ago?

　A tree will grow well in a climate (气候)with lots of sunshine and rainfall. And little sunshine or rainfall will limit (限制)the growth of climate by studying the tree rings. For example, to find out the weather of ten years ago, count the rings of a tree from the outside to the inside. If the tenth ring is far from the eleventh ring, then we’re sure that it was sunny and rainy most of that year. If it is near to the eleventh ring, then the climate that year was bad.

　Tree rings are important not only for studying the history of weather but also for studying the history of man. Many centuries ago there lived a lot of people at a place in New Mexico. But now you can find only sand there-no trees and no people. What happened?

　A scientist studied the rings of dead trees there. He found that the people had to leave because they had cut down all the trees to make fires and buildings. As all the trees had gone, the people there had to move.

4.Some comets keep coming back ________.

　A. at any time B. at noon C. at regular times D. at daytime

3.Maybe many people _______.

　A. haven’t seen any comets B. have seen all comets

　C. have seen a comet at daytime D. have seen a comet

2.A large part of a comet is ______.

　A.water and rock B. water frozen into pieces of ice and mixed with iron

　C. ice, iron and rock dust D. only a few big pieces of rock

1.A comet is like ________.

　A. sun B. moon C. sunlight D. the earth

5.What is the main idea of the passage?

　A.Animals move to find food more easily.

　B.The migration of the fish called “salmon” is the most famous migration.

　C.Living things move from one place to another because they like to travel.

　D. Sometimes we know why and how living things move from one place to another, but sometimes we don’t.

　Passage 2

　If you look at the sky one night and see something moving and shining that you have never seen before, it might be a comet (彗星).

　A comet sometimes looks like a star. Like a planet, a comet has no light of its own. It shines from the sunlight it reflects (反射). Like the earth, a comet goes round the sun, but on a much longer path (轨道) than the earth travels.

　If a comet isn’t a star, what is it then?

　Some scientists think that a large part of a comet is water frozen into pieces of ice and mixed with iron and rock dust and perhaps a few big pieces of rock. When sunshine melts (融化) the ice in the comet, great clouds of gas go trailing after it. These clouds, together with the dust, form a long tail.

　Many people perhaps have seen a comet. However no one knows how many comets there are. There may be millions of comets, but only a few come close enough for us to see.

　An Englishman named Edmund Halley, who lived from 1656 to 1742, found out a lot about the paths that comets take through the sky. Some comets move out of our sight and never come back. Others keep coming back at regular times. A big comet that keeps coming back was named after Halley because he was the one who worked out when it would come back again. Maybe you have ever seen Halley’s Comets because the last time it came close to the sun and the earth was in the year 1986. Then people all over the world were outside at night to look at it. You will probably be able to see Halley’s Comets when it comes near the earth again.

4.The lobsters move ________.

　A. to the fresh water B. at a certain time C. to the undersea D. to find more food

3.The mice in northern Europe move when _______.

　A. they give birth B. the place gets too crowded

　C. the weather is bad D. they haven’t enough food