The correct answer is: All of the above.
The planned layout, drainage systems, and standardized weights and measures found in Harappan cities suggest that the Harappans had a sophisticated urban planning system, a centralized authority, and extensive trade networks.
The planned layout of Harappan cities suggests that the Harappans had a sophisticated understanding of urban planning. The cities were laid out in a grid pattern, with streets running north-south and east-west. This grid pattern made it easy for people to get around the city and for goods to be transported.
The drainage systems found in Harappan cities suggest that the Harappans had a centralized authority. The drainage systems were designed to collect and remove wastewater from the cities. This required a high level of coordination and planning, which suggests that the Harappans had a centralized authority that was able to oversee the construction and maintenance of the drainage systems.
The standardized weights and measures found in Harappan cities suggest that the Harappans had extensive trade networks. The standardized weights and measures made it possible for traders to exchange goods easily. This suggests that the Harappans had extensive trade networks that allowed them to trade with other cultures.
In conclusion, the planned layout, drainage systems, and standardized weights and measures found in Harappan cities suggest that the Harappans had a sophisticated urban planning system, a centralized authority, and extensive trade networks.