过去进行时的变化规则如下：

一般规则

动词原形后直接加-ing，例如：look-looking，cook-cooking，read-reading。

以不发音字母e结尾的动词

去掉e再加-ing，例如：write-writing，live-living。

以重读闭音节结尾且末尾只有一个辅音字母的动词

双写该辅音字母后再加-ing，例如：begin-beginning，swim-swimming，sit-sitting。

少数几个以ie结尾的动词

要变ie为y，再加-ing，例如：tie-tying，die-dying，lie-lying。

过去进行时的例句：

肯定句

I was reading when she came.

They were playing basketball when it started raining.

I was studying English at 9pm last night.

否定句

She wasn’t doing anything at that time.

They weren’t watching TV when the power went out.

She was not studying last night.

疑问句

Were they working when you arrived？

Was he playing soccer with his friends？

Was/Were you studying when I called you？

这些规则和例句可以帮助你更好地理解和运用过去进行时。