"Yes, that sentence is correct."
Translation:Kyllä, tuo lause on oikein.
I think they should accept this one as an answer as well, but here's still my explanation of the difference:
tuo = that VS. se = it/the
So sometimes you can translate "Kyllä, se lause on oikein." into "Yes, the sentence is correct." But all this hassle with articles and no articles and demonstrative pronouns is a bit confusing even for me as a Finn and I actually find it much harder to translate into Finnish than from Finnish because I have to think about how to "translate" the articles and such all the time and there isn't always just one correct answer to these, especially without any proper context.
"Oikein" is an adverb and "oikea" is an adjective. "Oikein" is apparently also the superlative of the latter but I've never actually realized that before reading it from a dictionary (and I'm a native Finn!).
The difference of these words with the phrase in the exercise:
- Tuo lause on oikein. = That phrase is correct.
- Tuo lause on oikea. = That phrase is the correct one.
- Tuo on se oikea lause. = That is the correct phrase.
(I left out "Tuo on oikea lause." because it sounds more like "That is an actual phrase." because you can also use 'oikea' to basically brag that what someone did is nothing compared to what you or someone else can do.)
'That sentence' can be translated as 'se lause'. 'Tuo' refers to things you can point at, 'se' would be used for things you cannot point at (in general). Unfortunately they both translate as 'that' in English. 'The sentence' is not specific enough to be translated as 'se lause'. 'The sentence', certainly in the majority of the instances, would simply translate as 'lause'.