Which Statement Is MOST Accurate Given the Text's Discussion of the Gate-Control

Which statement is MOST accurate given the text's discussion of the gate-control theory of the experience of pain?

A) The pain gate is always opened and closed by bottom-up mechanisms..
B) The pain gate is always opened and closed by top-down mechanisms.
C) The pain gate is opened by bottom-up mechanisms; it may be closed in either a top-down or a bottom-up fashion.
D) The pain gate may be opened or closed by either bottom-up or top-down mechanisms.