Question

We are travelling by train. (add a question tag)​

Answer 1

We are travelling by train, aren't we ?

BASIC RULES FOR QUESTION TAG

If the statement is negative, the tag must be positive. If the statement is positive the tag must be negative.

The tense of the tag is determined by the tense of the auxiliary/modal verb of the statement that precedes it.

Answer 2

Answer:

We are travelling by train, aren't we ?