What is meant by "citing a source"?

remembering where you found the material
naming the source of the information
keeping the note card on file
none of the above

Excerpt from an enemy of the people henrik ibsen mrs. stockmann. (turns to the hall door, listening.) i expect that is mr. hovstad coming. billing. very likely. (peter stockmann comes in. he wears an overcoat and his official hat, and carries a stick.) peter stockmann. good evening, katherine. mrs. stockmann (coming forward into the sitting-room). ah, good evening--is it you? how good of you to come up and see us! peter stockmann. i happened to be passing, and into the dining-room). but you have company with you, i see. mrs. stockmann (a little embarrassed). oh, no--it was quite by chance he came in. (hurriedly.) won't you come in and have something, too? peter stockmann. i! no, you. good gracious--hot meat at night! not with my digestion, when peter stockmann enters, what does his physical appearance to reveal about his character?