Jiang Fei, a traffic officer in Bishan, said that the lighting system was very useful in the evenings and on rainy and foggy days.

璧山市交警姜飞说，照明系统在夜晚和雨雾天气非常有用。

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As often as not the buses are late on foggy days.

每遇多雾天气，公共汽车往往脱班。

《新英汉大辞典》

Many researchers theorized that Viking sailors found the sun on foggy days by using sunstones.

许多研究人员推测，在大雾天，北欧海盗水手们借助日长石寻找太阳。

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And though our crystal ball is rather foggy, we can say this for sure: If an end-of-days countdown has begun, then this week's escape is your best last chance to explore the cradle of Mayan civilization.

BBC: Daily deal: A Guatemalan escape