Which of these choices displays proper use of parallel structure and commas?
A) Our teacher informed us that we needed to study, that we needed to be vigilant about grades, and to take our work seriously.
B) Our teacher informed us to study more, that we needed to be vigilant about grades, and that we needed to take our work seriously.
C) Our teacher informed us that we needed to study, that we needed to be vigilant about grades, and that we needed to take our work seriously.
D) Our teacher informed us, that we needed to study, that we needed to be vigilant about grades, and that we needed to take our work seriously.