Translation:Anns an Fhionnlainn.
The preposition ann an in changes to anns before definite articles an, am, a’, na:
- ann am bàta in a boat but anns a’ bhàta in the boat,
- ann a’ phàirc in a park but anns a’ phàirc in the park,
- ann an coilltean in woods but anns na coilltean in the woods.
And since Finland in Gaelic is an Fhionnlainn, lit. the Finland with the definite article, you need anns an Fhionnlainn for in (the) Finland.
Unfortunately, a wee mistake was made in Tree 1 so the answer reads as "Ann am Fionnlainn."
The correct translation of this sentence is "Anns an Fhionnlainn."
Finland is An Fhionnlainn in Gaelic, and not 'Am Fionnlainn'. Sorry for the confusion, but both will be accepted here, and it will be fixed in Tree 2 :)
san Fhionnlainn is a shortened anns an Fhionnlainn and also acceptable. Probably Duolingo decided that whatever you’ve written is closer to that answer and that you probably intended to write it, so it displayed it as a correct one to you.
Both anns an Fhionnlainn and san Fhionnlainn are OK.
anns an, anns a’ and anns na may be shortened to san, sa, and sna respectively.
Anns am is wrong, it does not appear anywhere. It’s either ann am (before BFMP) / ann an (otherwise) for simple in or leniting anns a’ (before PBCGM) / anns an (otherwise) for in the.
Here it should be anns an Fhionlainn (because Finland is an Fhionlainn in Gaelic, lit. the Finland) but the exercise initially used ann am Fionlainn (just in Finland, without the the in Gaelic, notice no lenition).
What you wrote, anns am, could never happened because an changes to am only before the unlenited consonants BPFM and the definite article in dative (the an after anns is exactly that, the article) lenites (regardless of gender). So BPFM don’t appear after it, as they get lenited (like here: anns an Fhionlainn).
- anns a’ bhàta (in the boat) vs ann am bàta (in a boat),
- air a’ bhòrd (on the table) vs am bòrd (the table).
Also, reads the comment above.