There have been at least four major ice ages in the Earth's past.

至少有四个主要的冰河，在地球的过去。

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Piano training of young children can begin around the ages of three to four.

幼儿的钢琴训练从三至四岁就可以开始了。

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Piano training of young children can begin around the ages of three to four.

幼儿的钢琴训练从三至四岁就可以开始了。

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