我们正在吃午饭时，火警响了。
We were having lunch when the fire alarm went off.
▼点击显示答案
were英 /wɜː/|美 /wər/
having英 /ˈhævɪŋ/|美 /ˈhævɪŋ/
解释
过去进行时 were having 说明主事件 went off（火警响起）发生时正在进行的背景活动。吃午饭是持续的背景动作，火警响起是瞬间发生的打断事件。
We were having lunch when the fire alarm went off.
过去进行时 were having 说明主事件 went off（火警响起）发生时正在进行的背景活动。吃午饭是持续的背景动作，火警响起是瞬间发生的打断事件。