“在前线”常见的英文表达是 "at the front line" 或 "on the front line"，两者意思相近，均可使用。例如：
Soldiers are fighting at the front line.（士兵们在前线战斗。）
Many doctors and nurses worked on the front line during the pandemic.（疫情期间，许多医生和护士奋战在前线。）
此外，"in the front lines" 也是一种表达方式，但更侧重于描述身处冲突或斗争的核心区域。例如：
Journalists often find themselves in the front lines of dangerous situations.（记者们常常身处危险局势的前线。）
选择哪种表达方式取决于具体语境和想要强调的侧重点。