The correct answer is C. Reference Pronoun.
Explanation:
The pronoun is used to replace the noun in a sentence. The pronoun can be placed as a reference when the noun was previously mentioned. In this particular case, the word "Them" is a reference to the words " Supernatural beings". So, in order to avoid the repetition of these words, we use the reference pronoun.
Cool. Do you have a question though?
WhichWhish Question Are You Refering to?