2 sentences for 开封 (kāi​fēng — unseal)

1. 这瓶果汁已经开封了。

   zhè píng guǒ​zhī yǐ​jīng kāi​fēng le.

   This bottle of juice has already been opened.

   Source: Dong Chinese Dictionary

2. 开封后的牛奶请务必冷藏。

   kāi​fēng hòu de niú​nǎi qǐng wù​bì lěng​cáng.

   Please be sure to refrigerate the milk after opening.

   Source: Dong Chinese Dictionary