Because that's singular (Koń jest duży), and the sentence is about plural.
Nouns in plural take the same adjectival ending of neuter nouns in the nominative case?
I wrote the horses are big and it was incorrect 'cause is without "the" c'moooon
When making a word a plural (eg jałko to jałki) do you just replace the o (as in ocelot) with a i (as in india) at the end? Thanks.