题目内容
根据句意在下列各句空缺处写出各单词的正确形式
Many ________ (十亿) of years have passed, and great changes have happened on the earth.
答案：billions
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题目内容
根据句意在下列各句空缺处写出各单词的正确形式
Many ________ (十亿) of years have passed, and great changes have happened on the earth.