Question

how long--he--there?he---there for three days

Answer 1

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　　How long has he been there?

　　He has been there for three days.

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Answer 2

How long (-did-) he (stay) there?

He (stayed-) there for three days .

stay 为延续性动词,因此其一般过去时可同一段时间连用.

句意:他在那儿停留了多久?
他在那儿停留了三天.