问题描述：
1 He began to write poems in his thirties.
问：最后为什么用thirties而不用thirty?
2 When he moved to England in the fifties,he was already in his forties.
问：为什么fifty和forty都用复数?
3 A nucleus is about one millionth the size of an atom.
问：为什么用millionth而不用million?
问：最后为什么用thirties而不用thirty?
2 When he moved to England in the fifties,he was already in his forties.
问：为什么fifty和forty都用复数?
3 A nucleus is about one millionth the size of an atom.
问：为什么用millionth而不用million?
问题解答：
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