题目内容：

Water had also appeared on the other planets like Mars but, 1. the earth, it had disappeared later. It was not immediately obvious2. water was to be 3. to the development of life. 4. many scientists believe is that the continued5. of water allowed the earth to dissolve harmful gases and acids into the oceans and seas.

That afternoon 6. the train, the cousins 7. in their seats. Earlier that day, when they crossed the Rocky Mountains, they 8. catch sight of some mountain goats and even a grizzly bear and an eagle. …… Many of them have a 9. for riding wild horses and can win thousands of dollars in 10..