Mr dd dd
The subject of a sentence may be what parts of speech?

Traditional grammar classifies words based on eight parts of speech: the verb, the noun, the pronoun, the adjective, the adverb, the preposition, the conjunction, and the interjection.

Only a noun or a pronoun may be a subject of the sentence. Remember that there are assumed nouns and pronouns. Example: The sentence reads "Help!"
The context will set the subject.