"I had a salad for supper."
Translation:Mi ges i salad i swper.
"Ces" is the base form which can mutate softly to "Ges". It is always "Ges" in the interogative (Ges i afal i frecwast?) but in the positive you have a couple of choices and I'll explain the reasoning behind them. You can mutate it to "Ges i" which happens because there used to be a verbal particle before this sentence. There used to be one before the negative and interrogative too and these are e.g "Mi/fe ges i afal i frecwast" in the positive, "Ni ches i afal i frecwast" in the negative, note the drop of the "ddim" when the negative particle is used and "A ges i afal i frecwast?" in the interogative. The negative and interrogative verbal particles are never used nowadays as is "Fe" (almost, I have one teacher in my school who uses "Fe") which is from the south but "Mi" (The northern version) is still used quite often. Since you don't have to include "Mi/Fe" you can either leave the positive statement as "Ces i" or you can mutate it to "Ges i".
Yes, it was a mistake, apologies. Although 'Ces i' is a correct answer, the two forms taught here are 'ges i' (for South Wales) and 'mi ges i' (for North Wales). We included 'ces i' as an alternative for people studying Welsh in South West Wales to help them with 'English to Welsh' translations.
The contributor who wrote the question included too many possible 'best' translations which is why the system created a question with 'ces i'. That's corrected now. Thanks for the comment.