一发

zhè jiàn shì chǔ lǐ bù dàng jiù yī fā bù kě shōu shi le

这件事处理不当，就一发不可收拾了。

If this thing is mishandled, it's out of control.

nǐ xiān zhǔn bèi hǎo zī liào míng tiān yī fā dēng jì

你先准备好资料，明天一发登记。

You get the paperwork ready, and we'll register together tomorrow.

míng tiān bǎ nǐ de xìn hé wǒ de xìn yī fā jì chū

明天把你的信和我的信一发寄出。

Mail your letter alongside mine tomorrow.