Passerby a: Who knows, probably about to buy some ice-cream across the road?

路人甲：谁知道呢，兴许是要过路对面买冰淇淋什么的吧？

youdao

The 23-year-old's screams alerted a passerby who went to her rescue.

那名23岁女孩的尖叫声引起了一个过路人的警觉，他救了她。

《柯林斯英汉双解大词典》

You are supposed to look at a passerby just enough to show that you are aware of his presence.

当你观察一个过路人的时候，能够表明你意识到他的存在就可以了。

youdao

And the guy you just played a tape of there, he also told a passerby that we want to start a war in London.

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It is one thing for a passerby to observe or even to follow someone during a single journey as he goes to the market or returns home from work.

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When an old person wants to start a conversation with a passerby, most recognize the need.

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