哦

哦，原来是这样啊。

Ó, yuánlái shì zhèyàng a.

He encountered his old friend by chance.

哦，我明白了。

Ó, wǒ míngbai le.

By chance, they ended up together.

哦，你说的是那件事啊。

Ó, nǐ shuō de shì nà jiàn shì a.

I have traveled to Europe for tourism.