进行时的构成是：主语+be动词+现在分词～.

（现在分词的构成详见第六章）

1 现在进行时

I am watching TV now.

我正在看电视。

句型：主语+be（am，is，are）+现在分词～.

Look！Nancy is doing her homework

看！南希正在做作业。

They are cleaning their classroom.

他们正在打扫他们的教室。

2 过去进行时

He was walking in the park at that time yesterday

昨天那个时候，他正在公园散步。

句型：主语+be（was，were）+现在分词～.

I was watching TV then.

那时，我正在看电视。

When I came home， they were cooking in the kitchen.

当我进家时，他们正在厨房里做饭。