prosperity.

　　Increased climate variability(多变)from AD 250 to 600 coincided with the demise of the Western Roman Empire and the turmoil (动乱)of the Migration Period.

　　1．assumption n． 假定，假设　　

　　2．coincide v. 碰巧，同时发生

　　3．prosperity n. 昌盛，繁荣

　　4．productivity n. 生产力；生产效率

　　5．conflict n. 冲突，矛盾

　　1．What's the real cause of the Roman Empire collapsing according to scientists?

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　　2．Why is the rise and fall of empires associated with environmental change?

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　　【答案】　1.Climate change.

2．Because it affects water supply and agricultural productivity，human health and civil conflict.