Explanation
Correct answer: C.
Choice C is the best answer. The singular possessive pronoun "its" agrees with the singular antecedent "the animal" and indicates that the "young" belong to it.
Why the other choices are wrong
Choice A
Choice A is incorrect. This choice creates a pronoun-antecedent agreement error. "They’re" is a contraction of "they are," a plural pronoun and verb, but the antecedent "the animal" is singular. Also, we don’t need the extra verb "are" — we already have a main verb in this clause, so adding "are" would be confusing and ungrammatical.
Choice B
Choice B is incorrect. This choice creates a pronoun-antecedent agreement error. "Their" is a plural pronoun, but the subject of the sentence is "the animal," a singular noun.
Choice D
Choice D is incorrect. This choice creates a confusing and ungrammatical sentence. "It’s" is a contraction for "it is." We already have the verb "nurses" in this clause, so we shouldn’t add the verb "is."