卡普斯说，这是由于历史和地理原因。
Capps said there are both historical and geographic reasons for this.
在世界上的有些地区，暴露在自然辐射下的程度会因为当地的地理原因而不同。
In some parts of the world, levels of exposure to natural radiation differ due to differences in the local geology.
当然，这种情况一部分是由于历史和地理原因造成的：美国消费市场巨大，同时缺少类似欧洲那样的区域融合。
Certainly part of that is history and geography: America's own massive consumer market, and lack of regional integration (like Europe).
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