The scientific director may require an operator to demonstrate __________ and ability to properly operate the breath alcohol testing instrument.

The correct answer, proficiency, highlights the necessity for an operator to not only understand the theoretical aspects of using a breath alcohol testing instrument like the Intoxilyzer 9000, but also to consistently perform the testing accurately and effectively. Proficiency encompasses both the skill set and the knowledge required to operate the instrument, as it implies a level of mastery that ensures the operator can handle the equipment correctly under various circumstances. This quality is vital because accurate results depend on the operator's ability to execute all necessary protocols and procedures during the testing process.

While competence, skill, and knowledge are important attributes, proficiency specifically implies a higher standard of performance and a proven track record in using the device proficiently during actual operations, which is what the scientific director would prioritize during assessment.