Thomas Paine's central claim in this excerpt is that the distinction between kings and subjects is not a natural or religious distinction, but an artificial one that is worth questioning. Therefore, the correct answer is D) The differences between the kings and the subjects were not religious or natural.
Paine argues that the original equality among mankind could only have been destroyed by subsequent circumstances, and that the distinctions between rich and poor could be accounted for without having to resort to the explanation of oppression and avarice. He further states that the distinction between kings and subjects cannot be explained by natural or religious reasons, unlike distinctions such as male and female or good and bad. Paine believes that the origin of this distinction is worth investigating, and whether it leads to happiness or misery for mankind.
Therefore, option D is the correct answer to this question.