3. 现在分词和过去分词作状语时的用法比较。

不管是现在分词还是过去分词单独作状语，其逻辑主语必须与主句的主语一致。分词作状语通常可转换成一个相应的状语从句或并列句，如果状语分句或并列句中的谓语动词为被动结构，就用过去分词;如果状语分句或并列句中的谓语动词为主动结构，就用现在分词。例如：

When compared with the size of the whole earth , the biggest ocean does not seem big at all.

分词部分相当于When the biggest ocean is compared with the size of the whole earth, 主语与分词是被动关系，所以用过去分词。

When comparing it with the size of the whole earth, we find that the biggest ocean does not seem big at all.

When we compare it with the size of the whole earth... 主语与分词是主动关系, 所以用现在分词。

Faced with a bill for$10,000(=Because he is faced with a bill for$10,000), John has taken an extra job.

Whenever he was asked why he was late for class, he would answer carelessly, always saying the same thing (= and he would say the same thing).

注意：

1. 现在分词有两种时态：一般式doing和完成式having done。一般式通常表示与主句的谓语动词所表示的动作同时发生或无先后;完成式则强调分词所表示的动作先于谓语动词所表示的动作。如：

While walking in the street, we met some friends of ours.(同时发生)

Having waited in the queue for half an hour, Tom suddenly realized that he had left his wallet at home. (“等待”先于谓语动词“意识到”)

2. 分词的否定式的构成: not +分词。 Not having received a reply, he decided to write again.

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