如果发生问题，请马上告诉老师。

Rúguǒ fāshēng wèntí, qǐng mǎshàng gàosu lǎoshī.

If any problem happens, please tell the teacher right away.

昨天这里发生了一起小事故。

Zuótiān zhèlǐ fāshēng le yì qǐ xiǎo shìgù.

A small accident happened here yesterday.

不要去担心还没发生的事情。

Búyào qù dānxīn hái méi fāshēng de shìqíng.

Don't go worrying about things that haven't happened.