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My uncle has not been here for seven years.
我叔叔已有七年不在這裡了.

has (not) been表連續的狀態, 後面接無需限定的迄今一段時間, 故不加the; 如後面另有對seven years的限定詞語, 就要加the了 .

Helen has met many fiends during the seven years (while) she has been in America.
海倫在美國迄今的七年間, 遇見過許多朋友.

此句的she並不是大寫另起一句喔,  而是一個連接下來且省略關副while的形容詞子句. 這個子句對seven years有限定作用, 所以要加the.


結論:

加不加the只是限定或不限定, 與for或during無關.
我舉幾個反例, 您就明白了:

I have been staying home for the three days my wife has been away.
我老婆不在家到現在的三天期間, 我一直待在家.
這個three days帶有限定子句, 所以要加the, 前面卻是for. 

All employees should provide their opinions during a meeting.
在開會時全體員工都應踴躍提供意見.
這個meeting並不限定哪一次開會, 所以用a而不用the, 前面卻是during.

相信版主已有了清楚的概念了.