Final answer:
The word that best completes the sentence is 'elocution'.
Step-by-step explanation:
The word that best completes the sentence is elocution. Elocution refers to the skill of clear and expressive speech, which aligns with King George VI overcoming his stutter and mastering his speech. This word choice conveys the idea that he not only overcame his stutter but also became skilled in delivering speeches confidently and effectively.
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