front line
noun
(一般作the front line)
1- the military line or part of an army that is closest to the enemy前线, 火线：
as modifier the front-line troops.前线部队。
1.1
- the most important or influential position in a debate or movement（辩论、运动等的）关键位置, 关键地位, 第一线：
it is doctors who are on the front line of the euthanasia debate.
在关于安乐死的辩论中起关键作用的是医生。