The sirens warned the people of an impending attack by the enemy.

警报器警告人民敌人的攻击已经逼近了。

If you're experiencing crushing chest pain with or without pain in your left arm, are short of breath, or have a sense of impending doom, you may be having a heart attack.

如果你遇到伴有左手臂疼痛的强烈胸痛，或仅仅是强烈的胸痛，呼吸短促，或休克，你可能是心脏病发作了。