Read the passage, and then answer the question.
Archaeologists have dug up many weighing blocks that the Harappan people used in trade and commerce. The weighing blocks were standardized, which means they are all the same weight and size. The seals that the Harappans used for trade also tend to be uniform. They often have the same designs and patterns, even when they are found in cities that are miles apart. What can be concluded about the Harappan political system based on these discoveries?
A. Harappan cities were ruled by a powerful group of Harappan priests.
B. Harappan cities were ruled by an upper class of traders.
C. Harappan cities had a common authority that governed their trade.
D. Harappan cities were independent states with their own political systems.
E. Harappan cities were ruled by a powerful group of religious leaders and traders.