War(warm?)air is frequently lighter as the molecules bump around, excited by the heat.

暖空气经常更轻一些，因为分子受到热量的激励而四处碰撞。

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Since the beginning of the Cold War, international security crises have occurred frequently.

自冷战爆发以来，国际安全危机频频发生。

youdao

Since the beginning of the Cold War, international security crises have occurred frequently.

自冷战爆发以来，国际安全危机频频发生。

youdao