Castiel measured the participants' general violent tendencies in an attempt to control for ________.

A) participants' reactivity levels
B) extraneous variables
C) confounding variables
D) response bias

Castiel measured the participants' general violent tendencies to control for confounding variables, which are variables other than the independent variable that might cause the effect being measured, in this case, the relationship between autonomic responses and feelings of fear. By controlling for general violent tendencies, Castiel aims to ensure that any observed differences in fear or autonomic responses are due to the content of the video rather than participants' predisposition to violence.