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I have been in there for hours without seeing another person.

In the above sentence, 'in' seems redundent.

Since 'there' is adverb, I don't see any good reason there to be 'in'.

Can you teach me why?
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Normally, people say without 'in'
There is not enough context to answer. Perhaps the person has been stuck in a cell for hours.
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Hi,

It depends on context. Here is a scenario that dictates the use of in:
We arrived at the theater complex to see a movie. However, because all tickets were sold out, we could not get in. We were there (at the theater), but we were not in there. Therefore,‘in’ is used to further qualify our message.
Best wishes,
Hoa Thai
Oh, yes, it depends on the scenarios.

Didn't think about it, and haste to answer and learned a lesson here.
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The BELOW is the original sentence.

The library at the University of Maryland in College Park is so vast that I have been in there for hours without seeing another person.
Stenka25

I have been in there for hours without seeing another person.

In the above sentence, 'in' seems redundent.

Since 'there' is adverb, I don't see any good reason there to be 'in'.

Can you teach me why?

Students: We have free audio pronunciation exercises.
In which case, "in" is correctly used.
Thanks everyone.