d. the king has the potential to make his subjects happy.
Explanation:
"To the King's Most Excellent Majesty" is a poem written by Phillis Wheatley to honour and praise King George for his greatness and benevolence towards his people. In the lines "And may each clime with equal gladness see A monarch's smile can set his subjects free!", the poet uses the word free to suggest that the king has the potential to make his subjects happy.
This can be inferred from the use of the words "monarch's smile". It implies that the king has good intentions for his people and his smile has the power to make the people happy and contented.
