Definition: when something happens because of luck, or without being planned Level: B1
我在机场偶然遇到了一位老朋友。
I met an old friend ___by ___chance at the airport.
很凑巧，我需要的那本书正在打折。
___By ___chance, the book I needed was on sale.
我们很偶然地找到了那套完美的公寓。
We found the perfect apartment ___by ___chance.
