Question

Write the sentence, using 'have (has) been'/'have (has) gone'.

Answer 1

You could also say: “I was in Poland for a year” (That is more natural English)

Answer 2

If you want to incorporate 'for a year", you would need to say 'I have been in Poland for a year.'

But as 'been to' suggests just a visit and not a long stay, you may want to use "I had gone to Poland a year ago.'