Iso kissa on usein norjalainen.
How would you say "A big cat is Finnish"? How do you differentiate between a and the in Finnish
My guess is probably by context
Now that I know you don't need to bother with the or a, I sort of want to write "big cat is Finnish" because that works in English too. It won't let me though! :D
In English you need an article. It has to be either "a big cat" or "the big cat". If the article is lacking, Duolingo should not accept you.
Supporting Lassi492061, Wikipedia says this:
"English grammar requires that, in most cases, a singular, countable noun phrase start with a determiner. For example, I have a box is OK, but *I have box is not. The most common determiners are the articles the and a(n)"