Like quite a few German verbs that adjust their stem vowels, 'bieten' shifts from 'ie' to 'o' in Präteritum and to 'o' in Perfekt. We've got less than 48 hrs in Vienna over a Viking cruise. There are so many items I would like to do that I don’t see https://archerejnrw.wikirecognition.com/889569/little_known_facts_about_bieten