Why do some archaeologists believe that there was a single state in the Harappan society?

All of the above

Indications of the existence of an ancient authority/Single state:
Complex decision-making and implementation were observed within Harappan society, indicating advanced societal organization.
The uniformity of Harappan artefacts, including pottery, seals, weights, and bricks, is remarkable and suggests a high level of standardization.
Despite not being produced in a single centre, Harappan bricks maintained a consistent ratio across the entire region, from Jammu to Gujarat.
Settlements were strategically established in specific locations, indicating intentional planning and consideration of various factors.
The mobilization of labour was a significant aspect of Harappan society, particularly for brick-making and the construction of massive walls and platforms, highlighting the coordinated efforts and efficient organization within the civilization.