Scientists think that there has been life on Earth for   小题1: (百万) of years. However, we haven’t found life on other   小题2:  (行星) yet. The earth, the moon, and the sun are a small part of our galaxy. Scientists have   小题3:  ( 发现) many other galaxies in the universe. And there are many books about the universe. I’ve just finished   小题4: (看) a great book at school. It is a book about the solar system. It is so good that I’ve 小题5:   (已经) asked the library to keep the next book for 小题6: (我). In the book, it says that astronauts have    小题7:  (去) to Mars and even to Jupiter. I’ve never read that before. I’ve  小题8: (写信) to NASA to ask them for  小题9: （更多）information about astronauts and space. I hope they will write    小题10:  (回) soon.

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