Wundt's Method of Experimental Introspection Could Be Distinguished from Other

Wundt's method of experimental introspection could be distinguished from other forms of introspection because

A) Wundt used laboratory apparatus to standardize the presentation of stimuli to which subjects would respond.
B) his meticulous and detailed record keeping of all laboratory procedures was used to empirically demonstrate results.
C) Wundt required his subjects to free-associate to stimuli.
D) it was more mathematical.