"Would you like coffee? Yes."
Translation:Faset ti'n hoffi coffi? Baswn.
This involves a reply. It's not clear that it's two people speaking. This doesn't work well for duolingo.
Because of the wide range of yes/no responses in Welsh, the only realistic way to learn them all is by a question and response as in the example. We shall have to see if this can be made more obvious somehow.