50. I felt too tired and sleepy to go any____(far).
Ⅵ. 综合填空。(5分)
用方框中所给单词的适当形式填空。
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Scientists think that there has 51 life on the earth for millions of years. 52 , 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 53 the solar system. 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 54 many other galaxies in the universe. They are a long way away and their light has 55 for many years to 56 us. It’s hard to 57 how large the universe is.
Scientists have 58 lots of spacecrafts to visit other planets in our solar system, and some spacecrafts have gone 59 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 60 to send information to us? Are we alone. Is there life out there in space? We don’t know.