How did the Tang people gain the Mandate of Heaven? Song rulers grew weak and quarreled among themselves.
Arab traders took over the Silk Road trade, which undermined the Tang economy.
Tang invaders from the far north overthrew the Sui dynasty.
A Sui official led a rebellion that caused the Sui dynasty to collapse

Song rulers grew weak and quarrel among themselves. Arab traders took over the silk road trade, which undermined the tang economy. Tang invaders from far North overthrow the sui dynasty

i think it is a system for harvesting crops more easily

c.

worked constantly and gave many sincere speeches about the importance of independence