Question

A simple subject can be either a noun or a/an

Answer 1

It's a pronoun. The subject of a sentence could be I, him, her, etc considering the total idea of description, but it could not be to help(v), soft(adj), or softyly(adv). The subject must be an actual thing, not a description or action.

Answer 2

(B) pronoun

A simple subject can either be a noun or a pronoun.