The correct answer is option 'D' - theocratic-unitary.

The Harappan civilization, also known as the Indus Valley civilization, existed around 2600 to 1900 BCE in what is now modern-day Pakistan and northwest India. Although there is limited information available about their political structure, the material evidence suggests that their polity was theocratic-unitary.

1. Theocratic:
The term "theocratic" refers to a system of government in which religious leaders hold the highest authority and play a central role in the political decision-making process. The Harappan civilization had a strong religious belief system, as evidenced by the presence of numerous religious structures, such as the Great Bath and the Great Granary. These structures indicate that religion played a significant role in their society, suggesting a theocratic system of governance.

2. Unitary:
A unitary system of government is one in which power and authority are concentrated at the central level, with little to no autonomy given to regional or local entities. The Harappan civilization had a highly centralized political structure, with evidence of a well-planned and organized urban layout. The cities were built according to a grid-like pattern, with a central citadel or acropolis that housed important administrative and religious structures. The absence of significant regional variations in material culture suggests a strong central authority and a unitary system of government.

In conclusion, based on the material evidence available, the polity of the Harappan people was theocratic-unitary. Religious leaders held significant influence and played a central role in the decision-making process, while power and authority were concentrated at the central level, indicating a highly centralized system of governance.