Hi @wolfblue , I believe you can formulate this problem as seq2seq and use model such as T5 to solve this problem. You can give (dynamic number of) choices as contexts, and in fact by this method we can combine other type of QA (e.g. context-based [reading comprehension] QA) as augmented dataset too.
This approach results in SOTA in many datasets : https://github.com/allenai/unifiedqa 5