What part of speech are the words in sentence this is best birthday?

Here's the breakdown of the parts of speech in the sentence "This is the best birthday":

* This: Demonstrative Pronoun (points to a specific birthday)

* is: Verb (linking verb, connecting the subject "this" to the predicate "the best birthday")

* the: Definite Article (specifies a particular birthday)

* best: Adjective (describes the noun "birthday")

* birthday: Noun (the subject of the sentence)