In English, the definite article may mean in this sentence:
a specific box. It may be the manufacter's box, a box I found in the street, a box I made, etc. Example: The shoes are in the black box.
"in the box where the item was put right after manufactured, given to the buyer when it was bought". Example: The shoes are still in the box.
The context will make clear which meaning is intended.
in box is missing the article, which English requires, such as: in the box (or in a box)
On another point, sometimes Duolingo gives corrections to the wrong thing. So if Duolingo told you it should be plural, it might be wrong. It perhaps should instead have told you, there was a missing (definite) article.
For the plural there may be no article: in boxes is gramatically as good as in the boxes; the lack of an article may have caused the program to decide you intended to use a plural.
Yes. Italian omits the article in several place expressions. Some examples:
- Andiamo in montagna (We're going to the mountains)
- Stasera andiamo a teatro (We're going to the theater this evening)
- Accompagno Anna in aeroporto (I'm taking Anna to the airport)
- Andiamo in macchina (We're going in the/a car).
Odd! The speaker seems to say "Alcune sono ancore...". So that's what I wrote & it was accepted. Is ancore a correctly used word then? Haven't come across it so far. And what's the masculine version - ancori?