3 sentences

1. 大提琴的声音深沉而凝重。

   dà​tí​qín de shēng​yīn shēn​chén ér níng​zhòng.

   The sound of the cello is deep and solemn.

   Source: Dong Chinese Dictionary

2. 会谈现场的气氛非常凝重。

   huì​tán xiàn​chǎng de qì​fēn fēi​cháng níng​zhòng.

   The atmosphere at the meeting was very solemn.

   Source: Dong Chinese Dictionary

3. 他的神情凝重，仿佛在做重大的决定。

   tā de shén​qíng níng​zhòng, fǎng​fú zài zuò zhòng​dà de jué​dìng.

   His expression was solemn, as if he were making a major decision.

   Source: Dong Chinese Dictionary