平均每个美国人每年接收360毫雷姆的射线，其中300毫雷姆来自自然放射源，60毫雷姆来自人类活动(雷姆是射线强度单位)。
The average American receives 360millirems of radiation each year, 300 from natural sources and 60 from man-made activities. (a rem is a unit of radiation exposure.)
平均每个美国人每年接收360毫雷姆的射线，其中300毫雷姆来自自然放射源，60毫雷姆来自人类活动(雷姆是射线强度单位)。
The average American receives 360millirems of radiation each year, 300 from natural sources and 60 from man-made activities. (a rem is a unit of radiation exposure.)
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