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1. Will you be flying back or going by train?

2. Will you be flying back or going back by train?

Which is acceptable?

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anonymousWhich is acceptable?

Both.

Personally, in casual conversation I'd probably say

Are you going back by plane or train?

CJ

Comments  
anonymousWhich is acceptable?

They are both OK. I would ordinarily expect the first one.

 CalifJim's reply was promoted to an answer.