3 sentences

1. 他的文章辞藻华丽，但内容空洞。

   tā de wén​zhāng cí​zǎo huá lì, dàn nèi​róng kōng​dòng.

   His writing is ornate, but the content is hollow.

   Source: Dong Chinese Dictionary

2. 这篇报告辞藻华丽，但内容十分空洞。

   zhè piān bào​gào cí​zǎo huá​lì, dàn nèi​róng shí​fēn kōng​dòng.

   The report is flowery but devoid of substance.

   Source: Dong Chinese Dictionary

3. 由于长期的侵蚀，岩石内部形成了一个巨大的空洞。

   yóu​yú cháng​qī de qīn​shí, yán​shí nèi​bù xíng​chéng le yī gè jù​dà de kōng​dòng.

   Due to long-term erosion, a huge cavity formed inside the rock.

   Source: Dong Chinese Dictionary