1. A man was reading a newspaper on the seat of the subway train.

2. A man was reading a newspaper on the seat in the subway train.

3. A man was reading a newspaper on the seat on the subway train.

4. A man was reading a newspaper on the seat of the subway.

5. A man was reading a newspaper on the seat in the subway.

6. A man was reading a newspaper on the seat on the subway.
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Which expressions can we use? Would you check the sentences? Can we use both 'on' and 'in' before 'the train'?Thank you.

I think "on the seat" and "train" are not needed.

A man was reading a newspaper on the subway.

or

On the subway, a man was reading a newspaper.

All of the given sentences are grammatically correct and convey the same meaning. However, there are slight differences in emphasis based on the use of prepositions.

1. "A man was reading a newspaper on the seat of the subway train." - This sentence emphasizes that the man was reading the newspaper specifically on the seat inside the subway train.

2. "A man was reading a newspaper on the seat in the subway train." - This sentence also emphasizes that the man was reading the newspaper on a specific seat within the subway train.

3. "A man was reading a newspaper on the seat on the subway train." - This sentence suggests that the man was reading the newspaper on a seat that was located on top of the subway train.

4. "A man was reading a newspaper on the seat of the subway." - This sentence implies that the man was reading the newspaper on a seat that belongs to the subway but doesn't explicitly mention it being inside the train.

5. "A man was reading a newspaper on the seat in the subway." - This sentence suggests that the man was reading the newspaper on a seat located inside the subway but doesn't specify that it's on the train.

6. "A man was reading a newspaper on the seat on the subway." - This sentence implies that the man was reading the newspaper on a seat that is either on top of the subway or inside it but doesn't specify the exact location.

Regarding the use of "on" and "in" before "the train," both prepositions can be used depending on the intended meaning. "On the train" suggests being physically located on top of the train, while "in the train" suggests being inside the train.