"У мене немає сестри."
Translation:I do not have a sister.
Isn't сестри a plural form? I don't have sisters wasn't accepted as an answer. Instead it said I don't have a sister.
сестри in this context is the genitive singular for сестра.
In Ukrainian, with adverbs of quantity, for example - much (багато), мало (little) and none (немає) you use the genitive case.
But of course, in English it is more natural to say "I don't have any sisters."
сестри́ -> Genitive of сестра (singular)
се́стри -> Nominative plural
У мене немає сестри -> I don't have a sister.
У мене немає сестер -> I don't have sisters.
Duolingo should surely accept "I don't have any sisters," right? If not, then how would one say that in Ukrainian to differentiate it from "У мене немає сестри"?