4 sentences

1. 他说话的口气俨然是个大人。

   tā shuō​huà de kǒu​qì yǎn​rán shì gè dà​ren.

   He spoke in the tone of an adult.

   Source: Dong Chinese Dictionary

2. 他年纪不大，说话的口气俨然是个大人。

   tā nián​jì bù dà, shuō​huà de kǒu​qì yǎn​rán shì gè dà​ren.

   He is quite young, but he talks just like an adult.

   Source: Dong Chinese Dictionary

3. 他正襟危坐，神色俨然。

   tā zhèng​jīn​wēi​zuò, shén​sè yǎn​rán.

   He sat up straight with a dignified and solemn expression.

   Source: Dong Chinese Dictionary

4. 放眼望去，这里的街道整齐，屋舍俨然，十分宁静。

   fàng​yǎn wàng qù, zhè​lǐ de jiē​dào zhěng​qí, wū​shè yǎn​rán, shí​fēn níng​jìng.

   Looking out, the streets here are tidy, the houses are orderly, and it is very peaceful.

   Source: Dong Chinese Dictionary