when crossing street,you must be careful这句话,前后主语相同,前面的when是不是也要省啊

You must be careful when crossing the street.改为祈使句 Be careful when ( you are ) crossing the street. Look out when you______the street.A crossing B are crossing C cross D crossed when的省略用法 when crossing the street,it is nrcessary to be careful对不对 Be careful when your crossing the street.这个句子错在哪,Be careful when your crossing the street.这个句子错在哪, I saw him while he was crossing the street 与 He was crossing the street when i saw him 有什么区别 he was knocked down(when crossing the street).请问括号中为什么可以这样用? When he was crossing the street,a bike koncked him down什么意思 which side must passengers look first when crossing the street in London? The child was crossing the street when he suddenly-----[fall] to the ground. when crossing the street,the lady ------to the groundAfalls Bfell Chas fallen D had fallen 根据首字母填空：Be c___ to look both ways when crossing the street. when crossing street,you must be careful这句话,前后主语相同,前面的when是不是也要省啊 the old man was knocked down by a taxi when he was crossing the street请问这句用了哪些语法? [-A4] Look around when ______ the street.A.acrossB.crossedC.to be crossingD.crossing翻译包括选项并分析 _be careful when crossing the street.A.Must B.Should C.Ought to D.Do我选的是B, The old man with his son_______the street carefully when the traffic light was red.A.was crossing B.crossed Please be careful when you ______ the crowded street.这里是否只能填 cross?可不可以填 are crossing?如果不行,为什么呢?cross是短暂动词吗?