Rita conducts a study in which she videotapes college students interacting with each other before and after performing a series of cognitive tasks that were presented as "Intelligence tests that can affect your college tuition charges." She then has a carefully trained team observe and record the participants' actions, noting visible signs of anxiety in particular. What type of measure best describes the one used by Rita?

A. Physiological
B. Self-report
C. Behavioral
D. Statistical