4 sentences

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

3. 开封府是北宋时期的行政中心。

   Kāi​fēng fǔ shì Běi Sòng shí​qī de xíng​zhèng zhōng​xīn.

   Kaifeng was the administrative center during the Northern Song Dynasty.

   Source: Dong Chinese Dictionary

4. 这部小说描述了当年开封府的断案故事。

   zhè bù xiǎo​shuō miáo​shù le dāng​nián Kāi​fēng fǔ de duàn'àn gù​shi.

   This novel describes the case-solving stories of Kaifeng Prefecture from that era.

   Source: Dong Chinese Dictionary