Final answer:
Option (D), George Washington's experience as a soldier and commanding officer in the Continental Army was essential for his role as President and Commander-in-Chief, providing him with the necessary leadership skills and strategic insight.
Step-by-step explanation:
The essential qualities and experiences that George Washington needed as President and as Commander-in-Chief were strongly tied to his military background, particularly D. his experience as a soldier and commanding officer in the Continental Army. Washington’s leadership and strategic skills were honed during the Revolutionary War, which helped him as he sought to be an effective leader and to shape the role of the presidency.
Moreover, his experiences informed his choices, such as surrounding himself with knowledgeable cabinet members like Thomas Jefferson and Alexander Hamilton and focusing on the nation's security and economic development through careful thought on foreign policy challenges and internal improvements.