Why is the answer " An alive animal" not also correct . Een can mean "an " and the other meaning of levend is "alive'. In such a sentence there is surprise you have just stumbled across an alive animal....and you are exclaiming on such an event! In truth you are exclaiming because previously you thought it was dead. This meaning is this sense is not transferred adequately with the other two versions listed as correct. So I ask that my answer should also be considered as correct, please.
As a native UK the sentence "An alive animal" sounds no less odd than "A living animal". You would normally say "A live animal". I don't know if the Dutch means something else and this spoils translation or not tho.
Maybe... Although I think both are correct (I'm referring to living/live... Of course, it does sound a bit odd when said in the singular form...).
Anyway, I searched and I found this (brief) discussion: https://forum.wordreference.com/threads/live-animal-or-living-animal.573202/
It seems that to some speakers there's a difference in meaning between these words, live animals being perceived as animals that are right there, in front of you; and living animals as animals that are alive.