The replacement of ancient feudal dynasties in China was the result of land annexation. Long-term harmony must be divided, and long-term harmony must be achieved. Before the unification of China in the Tang Dynasty, warlords at the end of Sui Dynasty fought in melee. The long war reduced the labor force on the land. Ordinary people often have to move away to escape the war, or their families are torn apart or their families are destroyed. Therefore, throughout the ancient dynasties of China, natural disasters were always neglected first, with a small population in the early stage and a gradual increase in the later stage. As for whether the national policy has this effect. If the individual thinks that the policy is only a policy of restricting the benefit of the people, it is a policy of liberalizing the policy of restricting the benefit of the people, and it is a policy of increasing restrictions. Many dynasties generally recuperate and reduce taxes when the People's Republic of China is founded. = = This is the size of the population base that is liberalized, which mainly depends on the social productive forces and economic base in this period, and determines that the superstructure affects the economic base.

Therefore, choose B.