I knew the correct answer would be "Yes", but I tried "I am" because that is what I would naturally have answered to the question - as a speaker of English modified by Ulster dialect.
Oh sorry! That should have been accepted. I've added it now :)
There was such a long pause between the question, and the answer, that I typed out the translation for just the question and submitted it, not even hearing that the speaker had answered! And thus I was marked wrong.