课文填空。
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★ It was not immediately obvious that water was 1 the development of life.
★ This produced 2 , which made it possible for life to develop.
★ I earned my passage by working as an unpaid hand, which 3 .
★ When they crossed the Rocky mountain, they 4 some mountain goats and even
a grizzly and an eagle.
★ Many of them 5 riding wild horses and can win thousands of dollars.