7 sentences

1. 他始终战斗在科研第一线。

   tā shǐ​zhōng zhàn​dòu zài kē​yán dì​yī​xiàn.

   He has always worked on the front line of scientific research.

   Source: Dong Chinese Dictionary

2. 医护人员在抗击疫情的第一线。

   yī​hù rén​yuán zài kàng​jī yì​qíng de dì​yī​xiàn.

   Medical staff are on the front lines of fighting the epidemic.

   Source: Dong Chinese Dictionary

3. 海关人员坚守在保卫国门的第一线。

   hǎi​guān rén​yuán jiān​shǒu zài bǎo​wèi guó​mén de dì​yī​xiàn.

   Customs officers stand at the front line of defending the nation's borders.

   Source: Dong Chinese Dictionary

4. 医生们始终奋战在抗击疫情的第一线。

   yī​shēng men shǐ​zhōng fèn​zhàn zài kàng​jī yì​qíng de dì​yī​xiàn.

   Doctors have always been fighting on the front lines against the pandemic.

   Source: Dong Chinese Dictionary

5. 广大公安干警日夜奋战在维护社会治安的第一线。

   guǎng​dà gōng'ān gàn​jǐng rì​yè fèn​zhàn zài wéi​hù shè​huì zhì'ān de dì​yī​xiàn.

   The vast ranks of public security officers fight day and night on the front lines of maintaining social order.

   Source: Dong Chinese Dictionary

6. 敌人的进攻在第一线受挫。

   dí​rén de jìn​gōng zài dì​yī​xiàn shòu​cuò.

   The enemy's attack was thwarted at the front line.

   Source: Dong Chinese Dictionary

7. 将士们在战斗的第一线英勇奋战。

   jiàng​shì men zài zhàn​dòu de dì​yī​xiàn yīng​yǒng fèn​zhàn.

   The soldiers fought bravely on the front lines of the battle.

   Source: Dong Chinese Dictionary