过去进行时
由助动词be 的过去式 + 现在分词构成。其中be有人称和数的变化，第一、第三人称单数用was，其他用were.
1)过去进行时动词主要表示在过去某一时刻或某一段时间内正在进行或持续进行的动作。过去进行时经常与过去时配合使用。例如：
This time yesterday, we were having an English lesson. 昨天这个时候，我们正在上英语课。
The teacher was giving us a lesson when Tom walked into the room. 老师在给我们上课时，汤姆走进教室。
While we were having supper, all the lights went out. 我们吃饭的时候，灯灭了。
He was reading while she was setting the table. 她摆桌子时，他在读书。
It was getting dark. The wind was rising. 天渐渐黑下来了。风势增强了。
2)过去进行时动词常用always, continually, frequently 等词连用，表示过去经常发生的行为。这种用法表明带有的感情色彩。例如：
The two brothers were frequently quarreling when they were young. 两兄弟小时候常吵架。
In Qing Dynasty, China was always making concessions to western powers. 清朝时，中国总是对西方列强妥协。
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