过去进行时用来表示在过去某个时刻正在进行的动作，由be动词的过去式加动词现在分词构成。

Mike was having lunch when Terry arrived.

当特里到达的时候，迈克正在吃午饭。

They were reading books in the library at 3.30 this afternoon.

今天下午三点半的时候，他们正在图书馆里看书。

When the telephone rang, I was cooking a meal in the kitchen.

当电话铃声响起的时候，我正在厨房做饭。

请将下面每个句子中的错误改正，每题只有一处错误。

1. Sue is doing her homework at this time yesterday.

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2. My parents are preparing for my birthday party at 10 o'clock this morning.

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3. When I arrived home, my mother is cooking in the kitchen.

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4. I was sawing a film with my friends at that moment.

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5. What were you did when I knocked at the door?

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