在英语中，过去进行时用于描述在过去某一特定时间点或时间段正在进行的动作。为了识别和正确使用过去进行时，了解常见的标志词非常重要。以下是16个常用的过去进行时的标志词：
at that time（在那时）：用于指出一个具体的过去时刻，当时某个动作正在进行。
- Example: At that time, I was studying for my exam.
this time last year/month/week（去年/上个月/上周的这个时候）：用于回顾过去同一时间点的活动。
- Example: This time last year, we were planning our vacation.
from ... to ...（从...到...）：表示一个持续的时间段内发生的动作。
- Example: From 9 a.m. to 5 p.m., they were working on the project.
while（当...的时候）：引导从句，表示两个同时发生的动作。
- Example: While she was cooking dinner, he was watching TV.
as（当...的时候）：与“while”类似，但更强调两个动作的同步性。
- Example: As I was walking down the street, I saw a cat chasing a mouse.
during（在...期间）：指在某个特定时间段内进行的动作。
- Example: During the meeting, he was taking notes.
the whole morning/afternoon/evening（整个上午/下午/晚上）：表示一整天中某段时间的持续动作。
- Example: We were playing football the whole afternoon.
all day/night（整天/整夜）：强调一天或一夜中的连续动作。
- Example: She was sick and stayed in bed all day.
yesterday afternoon/morning/evening（昨天下午/上午/晚上）：具体指出过去的某一天中的某个时段。
- Example: Yesterday afternoon, I was reading a book.
last night/week/month（昨晚/上周/上个月）：表示过去的一段时间内发生的动作。
- Example: Last week, they were preparing for the conference.
earlier（早些时候）：指过去某个不确定但较早的时间点。
- Example: Earlier, I had been shopping for groceries.
suddenly（突然）：用于描述一个突然发生的事件，而另一个动作正在进行。
- Example: Suddenly, the phone rang while I was taking a shower.
just then（就在那时）：强调一个特定的、即时的过去时刻。
- Example: Just then, the door opened and he walked in.
in the middle of（在...中间）：表示在某项活动的中途。
- Example: In the middle of the lecture, he fell asleep.
around about（大约）：用于模糊地指出一个过去的时间范围。
- Example: Around about noon, we were having lunch.
between ... and ...（在...和...之间）：表示在两个时间点或事件之间的动作。
- Example: Between breakfast and lunch, I was working on my assignment.
这些标志词有助于识别句子中是否应使用过去进行时，并帮助读者或听者更好地理解叙述的过去情境。
