初中英语The fog was so thick-------the street lights were kept--

The fog was so thick_that_the street lights were kept__on___all day.
再问： 请问为什么是on all day.？我就是这一点很疑惑
再答： on 就是开的意思 off 就是关的意思 各种遥控器上 on/off 就是开关键。 找找你家里的遥控器。