The correct answer is A. Demonstrative pronoun
Step-by-step explanation:
In grammar, a pronoun is a word that replaces a noun or specific person, animal, object, etc. These pronouns can be of different types including personal pronouns such as the words she, he, they; indefinite pronouns such as all, both, nothing; relative pronouns such as the words who, which; interrogative pronouns such a what, when, where used in questions and demonstrative pronouns that are the type of pronouns that point out specific nouns and their location and include words such as this, that, those, these. Considering this, in the case of the sentence "This is the day I've been waiting for" in which the word in italics and the only pronoun is "this", the type of pronoun is demonstrative pronoun as this word replaces the noun "day" but also points out this word in terms of location in time, which occurs with demonstrative pronouns.