一、什么是过去进行时？

过去进行时用来描述在过去某个特定时间正在进行的动作或活动。它的结构是由“was/were + 动词-ing”构成的。

- 肯定句：主语 + was/were + 动词-ing形式。

- 否定句：主语 + was/were + not + 动词-ing形式。

- 疑问句：Was/Were + 主语 + 动词-ing形式？

例如：

- She was reading a book at eight o'clock last night.

- They were playing football when I arrived.

二、使用场景

1. 描述过去某一时刻正在进行的动作。

- 如：I was cooking dinner at six yesterday.

2. 表示过去某段时间内持续进行的动作。

- 如：He was studying English for two hours last night.

3. 与一般过去时结合使用，说明背景情况。

- 如：While I was walking home, it started to rain.

三、练习题

1. Complete the sentences with the correct form of the verb in brackets:

- I ______ (watch) TV when my mom came home.

- She ______ (talk) on the phone when the power went out.

2. Rewrite the following sentences in the negative form:

- He was playing basketball yesterday afternoon.

- They were watching a movie at nine o'clock last night.

3. Ask questions about the underlined parts:

- John was studying at the library last night.

- We were having lunch at twelve o'clock yesterday.

通过以上讲解和练习题，希望同学们能够更好地理解和运用过去进行时。语法的学习需要不断的练习和积累，希望大家能够在日常生活中多加应用，提高自己的英语水平。