Answer:
The correct answer is demonstrative pronoun
Step-by-step explanation:
Within a sentence, a demonstrative pronoun is used to point to something specific. Furthermore, a demonstrative pronoun replaces the noun into a sentence. There are four demonstrative pronouns: this, that, these, those, where this and that are singular, while these and those are plurals.
Bearing in mind the explained above, it could be said that into the sentence "This is exactly what I was talking about" the word this corresponds to a demonstrative pronoun since it not only points to something specific but also replaces the noun.