Answer is in the photo. I can't attach it here, but I uploaded it to a file hosting. link below! Good Luck!
tinyurl.com/wpazsebu
A "subject complement" is a word or a group of words that appears in the PREDICATE part of the sentence BUT refers to or describes the SUBJECT. "B" is the correct answer, because "better" describes the subject "I," even though it appears AFTER the verb "felt," which means it is in the predicate part of the sentence. Hope this helps!!
Correct me if I'm wrong but I believe it is phrase or clause containing three or more words at the beginning or end of a sentence.