Final answer:
The best definition of 'master' that fits the context is 'To acquire complete knowledge or great skill.'
Step-by-step explanation:
The best definition of 'master' that fits the context of the passage is option C, which is 'To acquire complete knowledge or great skill.' In the passage, Bert recognizes that in order to move to a more desirable sales management position, he needs to become highly skilled in client negotiations. This definition aligns with Bert's goal of becoming highly proficient in this area.
Learn more about Definition of 'master' in the context of the passage