7 sentences

1. 他在困难面前强自镇定。

   tā zài kùn​nan miàn​qián qiǎng​zì zhèn​dìng.

   He forced himself to stay calm in the face of difficulty.

   Source: Dong Chinese Dictionary

2. 尽量保持镇定。

   jǐn​liàng bǎo​chí zhèn​dìng.

   Try to stay calm.

   Source: OpenSubtitles

3. 请保持镇定。

   qǐng bǎo​chí zhèn​dìng.

   Please remain calm.

   Source: OpenSubtitles

4. 他表面上很镇定，实际上非常紧张。

   tā biǎo​miàn shàng hěn zhèn​dìng, shí​jì​shàng fēi​cháng jǐn​zhāng.

   He appears calm on the surface, but in reality, he is very nervous.

   Source: Dong Chinese Dictionary

5. 面对突发火灾，他表现得十分镇定。

   miàn​duì tū​fā huǒ​zāi, tā biǎo​xiàn de shí​fēn zhèn​dìng.

   He remained very calm in the face of the sudden fire.

   Source: Dong Chinese Dictionary

6. 面对警察的盘问，他表现得十分镇定。

   miàn​duì jǐng​chá de pán​wèn, tā biǎo​xiàn de shí​fēn zhèn​dìng.

   He remained very calm while being interrogated by the police.

   Source: Dong Chinese Dictionary

7. 虽然他表现得很镇定，但眼里的惊慌仍清晰可察。

   suī​rán tā biǎo​xiàn de hěn zhèn​dìng, dàn yǎn lǐ de jīng​huāng réng qīng​xī kě chá.

   Although he appeared calm, the panic in his eyes was still clearly detectable.

   Source: Dong Chinese Dictionary