3 sentences

1. 不要浪费，把剩菜放进冰箱里。

   bù yào làng​fèi, bǎ shèng​cài fàng​jìn bīng​xiāng lǐ.

   Don't be wasteful; put the leftovers in the refrigerator.

   Source: Dong Chinese Dictionary

2. 由于天气炎热，剩菜已经变质了。

   yóu​yú tiān​qì yán​rè, shèng​cài yǐ​jīng biàn​zhì le.

   The leftovers have gone bad because of the heat.

   Source: Dong Chinese Dictionary

3. 这些剩菜如果不及时倒掉就会发臭。

   zhè​xiē shèng​cài rú​guǒ bù jí​shí dào​diào jiù huì fā​chòu.

   These leftovers will stink if they aren't thrown away soon.

   Source: Dong Chinese Dictionary