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!!
This is something you’ll have to write yourself because it’s about you.
The answer is the last one, D. All of the other transitions indicate that the writer will either go into further detail on the subject or list other reasons as to why this would be correct. However, D clearly uses a contrasting transition to introduce a new argument.