理论上来说，游客每年仅有一次机会来参观这个坐落在一个军事单位中的直升机博物馆。
Theoretically, visitors can see this helicopter museum, placed in a military unit, only once a year.
美国每年有100亿农场动物专门供人食用，它们被看成是一个个生产单位，而不是有情的众生。
Viewed as production units rather than living beings with feelings, ten billion farm animals are exploited specifically for food in the United Statesevery year.
平均一个美国人每年要受到360毫雷姆(毫雷姆：核辐射量单位)的辐射，其中300毫雷姆来自自然界，60来自人类活动。
The average American receives 360 millirems 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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