士兵们在敌军防线后方执行任务时被俘。

The soldiers were captured during a mission behind ___enemy ___lines.

她自愿前往前线，展现了巨大的勇气。

She showed great courage by volunteering to go to the ___front ___line.

将军命令他的部队不惜一切代价守住防线。

The general ordered his troops to ___hold ___the ___line at all costs.