碘131有八天的半衰期，这意味着每八天其能量就下降一半。
Iodine 131 has a half-life of eight days, meaning that every eight days it loses half its strength.
亚马逊宣布其网上零售店收入稳定并预计了圣诞节的购物热潮，第二天其股价便上升了27%。
Amazon's share price shot up by 27% in a day after the online retailer delivered solid earnings and forecast a happy Christmas shopping season.
团队合作会随时间推移而改善：美国国家运输安全委员会发现，其民用航空数据库中，73%的事故发生在机组人员一起飞行的第一天。
Teamwork improves with time: America's National Transportation Safety Board found that 73% of the incidents in its civil-aviation database occurred on a crew's first day of flying together.
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