Scientists think that there has been life on Earth for millions 【小题1】planets (百万) of years. However, we haven’t found life on other discovered/found 【小题2】reading (行星) yet. The earth, the moon, and the sun are a small part of our galaxy. Scientists have already 【小题3】me ( 发现) many other galaxies in the universe. And there are many books about the universe. I’ve just finished been 【小题4】written (看) a great book at school. It is a book about the solar system. It is so good that I’vemore 【小题5】back (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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解析：
【小题1】此题考查不确切数量的表达方式，在hundred，million等词的复数后面加“s”表示不确切数量，故选millions.
【小题2】此题考查名词的复数形式，planet是可数名词，其他的行星就用other planets.
【小题3】此题考查动词的过去分词，因发现在英文中用两个单词来表示，find和discover，它们的过去分词形式是found和discovered。
【小题4】此题考查固定短语finish doing sth表示做完某事，故选reading。
【小题5】此题考查副词，在肯定句中，表示已经的副词用already。
【小题6】此题考查人称代词，因前面有介词for，故用宾格me。
【小题7】此题考查固定短语have been to 表示曾经去过某地，故用been。
【小题8】此题考查固定结构write to sb表示给某人写信，因用完成时，故用written。
【小题9】此题考查形容词的比较级more。表示更多的。
【小题10】此题考查固定结构write back表示回信的意思。