by chance 碰巧 偶然 一般接在句子后面
例句：I heard their talking by chance.
我偶然聽到他們的談話.
I met her quite by chance.
我遇見她完全是偶然的.
I won purely by chance.
我完全是僥幸打贏的.
come across v.偶遇；無(wú)意中發(fā)現(xiàn)；講得清楚明白；[口]給人…印象
偶然遇見 | (越過…而)來到 | 偶然碰見 | (無(wú)意中)碰到,找到,想到
例句：Perhaps I shall come across him in France.
也許我會(huì)在法國(guó)遇見他.
I came across this book in an old bookstore in London.
我在倫敦一家舊書店里發(fā)現(xiàn)了這本書.
Your speech didn't come across; nobody understood your opinion.
你的演說講得不明不白,沒有人能聽懂你的意思