Final answer:
The pillars of 'political prosperity' according to Washington were D. National unity and honesty, with him advocating for International isolation to avoid foreign conflicts and cautioning against the divisive effects of political parties.
Step-by-step explanation:
According to Washington, the pillars of "political prosperity" were D. National unity and honesty. As the first President of the United States, George Washington was keenly aware of the dangers of foreign entanglements and partisan fighting.
In his Farewell Address, he advised the nation to steer clear of permanent alliances with any portion of the foreign world, thus hinting at the concept of International isolation to avoid unnecessary conflicts.
Washington was also a proponent of national unity, warning against the divisive nature of political parties. Although he did not explicitly mention public education as a pillar, it could be implied that an educated electorate is necessary for the functioning of a healthy, democratic nation.