出门前记得把大衣的纽扣儿系好。

chūmén qián jìde bǎ dàyī de niǔkòur jì hǎo.

Remember to fasten the buttons on your coat before going out.

如果纽扣儿太松，你可以自己缝一缝。

Rúguǒ niǔkòur tài sōng, nǐ kěyǐ zìjǐ féng yì féng.

If the button is too loose, you can sew it yourself.

你衬衫的纽扣儿掉了一个。

Nǐ chènshān de niǔkòur diào le yí gè.

One button on your shirt has fallen off.