"You are guilty of being there."
Translation:Rwyt ti'n euog o fod 'na.
The full list is here :- https://www.duolingo.com/skill/cy/PresTens3
Simply the statements start with an 'r' ie rydw i, rwyt ti, rydyn ni, rydych chi (although in speech we drop the 'r' in everything except for 'rwyt')
The question form drops the 'r'.
So in the above 'Rwyt ti'n euog o fod 'na' = You are guilty of being there. Wyt ti'n euog o fod 'na? = Are you guilty of being there?