Great! I checked it out and the examples you listed there were both a great help and seem to confirm this definite/indefinite subject idea. Here's an explanation I found under Russian Grammar from our reliable friend Professor Wikipedia.
"There are no definite or indefinite articles (such as the, a, an in English) in the Russian language. The sense of a noun is determined from the context in which it appears. ... Word order may also be used for this purpose, compare "В ко́мнату вбежа́л ма́льчик" ("Into the room rushed a boy") and "Ма́льчик вбежа́л в ко́мнату" ("The boy rushed into the room")."
I answered "in the tree are birds" and it told me it was wrong. Not very pretty I admit but is it grammatically incorrect English?
ok I seriously have no idea when to use "the" and "a". Why is "there are birds on a tree" not accepted? The sentence is not clearly pointing any particular tree. I know in Slavic languages it is hard to establish this, since we dont use anything similar to distinguish nouns like in Germanic languages. Its just getting frustrating for me in these lessons :D :D Its probably a stupid idea but couldnt in these cases Duo accept both cases with definete and indefinete nouns? I dont know about Russian, but I know for sure that in Slovak and Czech and as far as I know in Polish too, the word order is not important in the sense of making the noun definete or indefinete. But maybe Im wrong. But as a native speaker of Slavic language I find this just as putting Germanic language grammar mindsetting into language where this aspect does purely just not exist. Correct me if Im wrong please.