At, call, try, discover, however, beyond, travel, send, be, understand, reach， good

Scientists think that there has    1    life on the earth for millions of years.    2   , we haven’t found life on other planets yet. Why?

The earth is a planet and it goes around the sun. There are other planets that also go around the sun. The sun and its planets    3    the solar system(太阳系). The solar system is a small part of our galaxy(银河系).

The stars we see at night are the suns in other solar systems. There are more than 200 billion stars in our galaxy, the Milky Way, and our sun is only one of them.

But scientists have    4    many other galaxies in the universe. They are a long way away and their light has    5    for many years to    6    us. It’s hard to    7    how large the universe is.

Scientists have    8    lots of spacecrafts to visit other planets in our solar system, and some spacecrafts have gone    9    the solar system. However, no one has discovered any life in space yet.

But why has no one from other planets sent us a message? Have they   10   to send information to us? Are we alone. Is there life out there in space? We don’t know.

1.___________  2.____________  3.____________  4.______________  5.______________

6.___________  7.____________  8.____________  9.______________ 10.______________

At, call, try, discover, however, beyond, travel, send, be, understand, reach， good

Scientists think that there has    1    life on the earth for millions of years.    2   , we haven’t found life on other planets yet. Why?

The earth is a planet and it goes around the sun. There are other planets that also go around the sun. The sun and its planets    3    the solar system(太阳系). The solar system is a small part of our galaxy(银河系).

The stars we see at night are the suns in other solar systems. There are more than 200 billion stars in our galaxy, the Milky Way, and our sun is only one of them.

But scientists have    4    many other galaxies in the universe. They are a long way away and their light has    5    for many years to    6    us. It’s hard to    7    how large the universe is.

Scientists have    8    lots of spacecrafts to visit other planets in our solar system, and some spacecrafts have gone    9    the solar system. However, no one has discovered any life in space yet.

But why has no one from other planets sent us a message? Have they   10   to send information to us? Are we alone. Is there life out there in space? We don’t know.

1.___________  2.____________  3.____________  4.______________  5.______________

6.___________  7.____________  8.____________  9.______________ 10.______________

  阅读短文，根据短文内容及首字母提示，在空白处填入一个适当的单词。

Scientists think that there has 66 b___life on Earth for 67m______ of years. However, we haven’t found lift on other 68p_____ yet. The earth is a planet and it 69g___ around the Sun. Seven other planets also go around the sun but 70n____ of them has life. The Sun and its planets are 71c___ the solar system. It is a small part of our galaxy. Scientists have 72d____ many other galaxies in the universe. They are a long way away and their light has 73t_____ for many years to reach us. It is hard to understand how large the universe is. Scientists have sent lots of spacecraft to look at other planets in our solar system, and some spacecraft have gone 74b____ the solar system. However, no one has discovered any life in 75 s_____ yet.

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.

1.A comet is like ________.

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

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

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

4.Some comets keep coming back ________.

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

5.Halley’s Comets came back _____.

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