"Argentina is a country."
Translation:Gwlad yw yr Ariannin.
Firstly, this particular sentence has been deleted from the course and should no longer be appearing at all - please let us know if it has come up recently.
Secondly, your question... The correct sentence would be:
- Gwlad ydy'r Ariannin - Argentina is a country
This is an emphatic statement with the identity/role of Argentina as gwlad (a country) coming first in the sentence, as is usual with any identifying sentence of this type:
- Sioned dw i - I'm Sioned
- Tad Sioned dw i - I'm Sioned's father
- Draig ydy e - He's a dragon
- Athro dych chi - You're a teacher
There is only one verb in each of those - dw, dw, ydy, dych respectively - and the identity/role of the person/thing is put first in the sentence.
In * Mae'r Ariannin ydy gwlad there are two verbs, mae and ydy, fighting for the same job, so that pattern is doomed anyway. * Mae'r Ariannin yn wlad with its single verb mae would work as a sentence, but it is of the wrong pattern for its purpose.
Mae'r Ariannin yn fawr would be correct for 'Argentina is big' - it is a descriptive sentence, not an identifying one.
Nearly all the sections of the course are accompanied by explanatory notes. We recommend that you read and perhaps copy them for ease of reference before starting each new section