3 sentences

1. 两人促膝谈心。

   liǎng rén cù xī tán​xīn.

   The two of them had a heart-to-heart talk.

   Source: Dong Chinese Dictionary

2. 我一生中，从没想过能看到你单膝下跪。

   wǒ yī​shēng zhōng, cóng méi xiǎng guo néng kàn​dào nǐ dān xī xià​guì.

   In all my life, I never thought I'd see you down on one knee.

   Source: OpenSubtitles

3. 膝盖骨位于膝关节的前方，起到了保护关节的作用。

   xī​gài​gǔ wèi​yú xī guān​jié de qián​fāng, qǐ​dào le bǎo​hù guān​jié de zuò​yòng.

   The kneecap is located at the front of the knee joint and serves to protect it.

   Source: Dong Chinese Dictionary