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Since 用来说明动作起始时间，for用来说明动作延续时间长度。例如： I have lived here for more than twenty years.我住在这儿二十多年了。 I have lived here since I was born. 我从出生起就住在这儿了。 注意：并非有for 作为时间状语的句子都用现在完成时。 I worked here for more than twenty years. （我现在已不在这里工作。） I have worked here for many years.（现在我仍在这里工作。） 注意：用句型转换的方法，很容易排除非延续动词在有for/since结构的完成时中的误用。 1）（对） Tom has studied Russian for three years. = Tom began to study Russian three years ago， and is still studying it now. 2）（错） Harry has got married for six years. = Harry began to get married six years ago， and is still getting married now. 显然，第二句不对，它应改为 Harry got married six years ago. 或 Harry has been married for six years. | 
