"Did I understand what they were talking about?"
Translation:Ddeallais i am beth o'n nhw'n siarad?
According to the multiple choice question you can use either ro'n or o'n? Can you always use the affirmative after beth, in other tenses as well? "Beth maen nhw'n siarad," for example?
It is not a matter of 'affirmative' or not. In many simple questions beth...? should be followed by ydy/yw, oedd, fydd, etc, but in this case the question is actually am beth...?, and this is followed by mae, roedd, bydd, etc (similarly with any case where a preposition precedes the beth or pwy as part of the question, as well as in certain other cases).
However, the r- of roedd, etc is often dropped in speech especially, so ...o'n nhw... is accepted here as well as the 'correct' ...r'on nhw....
It can get a little complicated to decide between the verb-forms to use after pwy and beth - don't worry about it too much as your meaning will always be understood.
I see. This question (which verb form to use after question words) is indeed one of the more difficult ones to get right… Does the phenomenon only happen if beth/pwy is preceded by am or is this a general rule valid for all prepositions? For example:
- I bwy (ydy/mae)’n rhaid dysgu hwnna?
- Gyda phwy (ydy/mae) e’n mynd ar wyliau?
- Ar feth (ydy/mae) hi’n gwrando?
- At bwy (ydy/mae)’r llythyr?
- Yn erbyn beth (ydyn/maen) nhw’n protestio?