题目内容
No one knows exact 1. the earth began, as it happened so long ago. 2. , according to a 3. (wide) accepted theory, the universe began with a “Big Bang” that threw matter 4. all directions. After that, atoms began to form and combine to create stars and other bodies.
Water 5. (appear) on other planets like Mars but, unlike the earth, it had disappeared later. 6. was not immediately obvious that water was to be fundamental to the development of life. What many scientists believe is that the continued 7. (present) of water allowed the earth 8. (dissolve) harmful gases and acids into the oceans and seas. This produced 9. chain reaction, 10. made it possible for life to develop.
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