Some say the answer is Endnote and some say the answer is Style Manual, but I can assure you that the answer is A) Footnote
Reason: I was taking a test a while ago and had the same question, I couldn't accept any answer other people gave so I took my own time re-studying. It was then when I found about a Footnote Citiation.
Definition:
Footnote Citation: an ancillary piece of information printed at the bottom of a page. (Ancillary means providing necessary support to the primary activities; aka the citation).
Your welcome! Don't fall for wrong answers anymore!