English question, please help?

" I have been a teacher for 10 years."
=> I have been a teacher for 10 years and I am now still teaching.

" I had been a teacher for 10 years."
=> I had been a teacher for 10 years, but I am not teaching any more.

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Q : Is there any difference between "have been" and "had been" ? Are they interchangeable?
A :
i) "Has/have been" --- Present Perfect Tense (現在完成式)
-- to be used to describe an action which has started in the past and is continuing till now.
eg. He has been ill since Wednesday.
　[ 他從星期三就一直生病 ] ----→ 表示現在仍然未痊癒

ii) "had been" --- Past Perfect Tense (過去完成式)
-- to be used to describe an action which had been completed /already existed in the past.
eg. He had been ill for a week when he went to a doctor.
　[ 他去看醫生之前，已經病了一個星期了 ] --→ 叙述一件 已過去 及 已 完成 的事

(#) "have been" & "had been" should be used in different occasions as an indication of the TIME for a particular moment / incident.
They should be used differently and should not be taken as the "same" thing at all.