Answer: I.
Explanation: a pronoun is a word that can function as a noun phrase used by itself and that refers either to the participants in the discourse or to someone or something mentioned elsewhere in the discourse. There are three pronoun cases: subjective (subject of the sentence: I, you, we, she, he, it, they, etc), objective (object of the sentence: me, us, him, her, whom, etc) and possessive (indicates belonging: his, her, theirs, mine, my, our, etc). In the given sentence the pronoun is in the subject of the sentence, so it should be "I."