how to use back then and at that time correctly

[kwfine]

Dear teachers,

Could you tell me the how to use back then and at that time correctly please?

I wrote a few sentences here. Please correct me if I am wrong.

1.
I went to the US 5 years ago.
I had been staying there for two months back then.

2.
I went to the US 5 years ago.
I had been staying there for two months at that time.

Thank you.

Kitty

[emsr2d2]

Dear teachers,

Could you tell me the how to use back then and at that time correctly please?

I wrote a few sentences here. Please correct me if I am wrong.

1.
I went to the US 5 years ago.
I had been staying there for two months back then.

2.
I went to the US 5 years ago.
I had been staying there for two months at that time.

Thank you.

Kitty

Neither of those are natural. If you say you went to the US five years ago, then you can't have already been staying/living there for two months at that time. The first part of your statement appears to introduce the beginning of your trip to the US so to suggest that you had already been there two months at that time doesn't fit.

I went to the US five years ago and stayed for two months.
I went to the US five years ago. At that time, I had only planned to stay for two months but I stayed for three years.

[billmcd]

Dear teachers,

Could you tell me the how to use back then and at that time correctly please?

I wrote a few sentences here. Please correct me if I am wrong.

1.
I went to the US 5 years ago.
I had been staying there for two months back then.

2.
I went to the US 5 years ago.
I had been staying there for two months at that time.

Thank you.

Kitty

Either one is acceptable in AmE, but with the past perfect continuous as in your examples one would expect a follow on statement such as, ".....when I received a message to return to my native country". If you simply want to state that you resided there for only "two months", why not use the simple past tense and you could still use "back then" or "at that time".

[kwfine]

Dear teachers,

what if I changed the sentence this way:

I went to the US 5 years ago.
I was a secondary school student at that time.

Is this correct?

[emsr2d2]

Dear teachers,

what if I changed the sentence this way:

I went to the US 5 years ago.
I was a secondary school student at that time.

Is this correct?

That's absolutely fine.