Im not sure if im correct or not but I think its C.
(please let me know if im wrong)
I hope it was helpful and sorry if I was wrong ^-^
Answer: All you have to do is write. anyways here's my discord name ill help you out thru there "Enigma#2888" if you want.
Explanation:
Major.
Because the subject of the sentence is "I", "major" is the subject compliment.
I hope I helped! :))