an area where the enemies are facing each other during a war and where fighting takes place 前线 Tanks have been deployed all along the front line. 整个前线全都部署了坦克。 - in/on the front line
The regiment was sent to fight in the front line. 这个团被派到前线作战。 front-line troops 前线部队
the most important position in a debate or an area of work 在最重要的岗位上;在第一线 - in the front line (of something)
a life spent in the front line of research 在研究的第一线度过的一生 - on the front line (of something)
They are on the front line, talking to the customers about our products. 他们在第一线,和顾客谈论我们的产品。
- in the front line (of something)