Because of these fluctuations, estimating the annual mean concentration of radon in indoor air requires measurements of mean radon concentrations for at least three months.
鉴于这种起伏，估算室内空气中氡的年平均浓度需要对氡的平均浓度至少进行三个月的测定。
2
Wine — and, in particular, red wine with its high concentration of the chemical resveratrol from the grape skin — is anti-cancer and pro-heart, at least in moderation.
适量的葡萄酒——特别是葡萄皮中含有大量化学物质白藜芦醇的红葡萄酒——具有抗癌和有益心脏的作用。
3
We know from studying ancient Antarctic ice cores that this concentration is higher than it has been for at least the past 650, 000 years.