This is literally the first full sentence I have translated correctly in Vietnamese without dictionary hints XD
why can't you say CAC co gai o nha ga? Why is it NHUNG? What's the difference?
"các" and "những" are the same when we tell about somebody or something, but "các" is the most appropriate word used in dialogue or conversation. For instance, "What are you guys going to do?" = "Các bạn dự định sẽ làm gì?"
The little girls are at the train station should be acceptable too if previous lessons are gong to translate "co gai" as "little girls"
you would normally use "cô gái" for girls whose age range is from their teenage to their twenties, arguably to their mid-thirties, usually unmarried.
in = "ở trong nhà ga" = to be physically inside the train station. While one can argue the two "ở" and "ở trong" are similar, there is a difference when you say you're at someone's house (at the front door) and you're inside someone's house.
The other difficulty is that prepositions like "in" don't always have consistent usages within a language (at least not in English). If we say "in the fridge" we mean inside the fridge, and if we say "on the fridge" we mean in physical contact with the fridge (usually with the top of the fridge, but not always--"the magnets are on the fridge" doesn't mean the magnets are on top of the fridge). But if we say "He's on the plane" or "on the bus" or "on the train" we mean he's inside the plane/bus/train, not outside and on top of it. One might think we use "on" as "inside" for vehicles or transportation, but that is not the case, since we don't use "on the car" to mean "inside the car"--we use "in the car" for that.
In Italian, the preposition usually translated "from" is often used to indicate being "at" or "to" (whether inside or not) the house or dwelling of a person.
That's what I typed. And it's definitely correct. Too bad Duolingo doesn't think so. :(