"그 소년들이 사과를 먹어."
번역:The boys eat an apple.
Duolingo wants to teach the explicit plurals and definite articles of English. So it enforces these plurals and articles in the Korean translation. It can be tricky, too. ^^
i understand what you mean but 'the boys eat an apple' this sentence is so tricky cause 'the boys' will not be full with 'an' apple.