[译] 我们时刻都要划清敌我界限。
[误] We must draw a clear line between enemies and ourselves at all times.

[正] We must draw a clear line between the enemy and ourselves at all times.
[注] enemy 可以作可数名词用，但泛指“敌人”或“敌军”时，应该用单数形式，属集体名词，表示复数意义，且前面用定冠词。如：A successful man often has many enemies.一个成功的人往往有许多敌人。