"What is your name, teacher?"

Translation: Dè an t-ainm a th' oirbh, a thidseir?

[KathyrynMa]

why is it sometimes 'thidseir', and sometimes 'a thidseir'? Or 'sheanair' / 'a sheanair'? didn't see an explanation between the two, just sometimes it marks it wrong no matter which way I put it. Or is it just a bug in Duolingo?

[cafeamor]

why is it sometimes 'thidseir', and sometimes 'a thidseir'? or athair and a athair? when the english is exactly the same.