The concept of centralizing governmental power. In this process, large amounts of land and people come under the control of a single government. What might be the advantages to a society that centralizes its government (such as the Sui Dynasty in China) compared to a decentralized system (such as Ancient Greece)?

The advantages of a centralized government impliy the following.
After the industrial revolution, the growth of economics worldwide has been lead by large companies that need centralization to be effective.
But in ancient times like the dynasties in China, a central government unified people in order to have a better control of the society. A strong central authority made possible a much better internal operation of rules.
However, centralization has disadvantages like despotism, autocracy and deaf ears to peoples opinions and demands.
In decentralized systems like the Greeks of ancient times, The Assembly had monthly meetings in Athens to discuss the the problems of the city. The meetings were open to the public in a demonstration of civility and the right of hearing to anyone.
Nowadays we find decentralized governments like the U.S. or centralized ones like Cuba.

Im pretty sure the answer is d.) is more densely populated.

Possess private property.