chance前的介詞用by,例如:
1、Several years after they'd split up they met again by chance in Paris.他們分手幾年以後在巴黎又偶然相遇。
2、I saw the letter purely by chance.我看見這封信純屬偶然。
3、I met her by chance at the airport.我碰巧在機場遇見她。