Pick the most appropriate auxiliary verb to fill in the blank:
CCTV _______ been used for many years for the surveillance of public areas associated with obvious risk.

The use of "has" as the auxiliary verb in this sentence is appropriate because it indicates an action that started in the past and continues into the present. The phrase "for many years" suggests a duration of time, indicating that the use of CCTV for surveillance has been ongoing. The auxiliary verb "has" is used with the third-person singular subject "CCTV" to form the present perfect tense, which is suitable for describing an action that began in the past and has a connection to the present.

The correct option is C.