do you mean min, mit and mine? min is for common 'n' words, mit is for neuter 't' words, and mine is for more than one. So if it was 'Dit dyr spiser ____ aeble' then it would be 'mit' but because it is more than one it is instantly 'mine'. Im pretty sure thats it, if not feel free to pull me up.
How do you know that they the singular dyr is being used instead of the plural? I put in "Your animals are eating my apples", which was marked incorrect but I was under the impression that dyr is both used as a singular and a plural. Is this a duolingo error or a logical error on my part?
Although the word "dyr" doesn't change between singular and plural, there are usually other clues as to whether or not it is plural. In this sentence, what makes it singular is the use of "dit",. "dit" is used with singular, neuter words. If it were plural, the word you would replace "dit" with is "dine", used with all plural nouns
Based on the possessive pronoun used.
In short, the possessive pronoun's form must reflect the noun's number and gender, and "dit" is one of the two possessive pronouns for singular nouns, so we conclude that dyr must be singular.
Possessive pronouns are discussed in "Tips and notes" for the "Pos. Pron." skill.
"dit dyr" -> "your animal"
"dine dyr" -> "your animals" (dine is a possessive pronoun for plural nouns, so we conclude that dyr is plural)