Why was the Grand Canal such an essential part of China's economic health?
a. It helped to stop flooding of the Hwang He and therefore allow for more food production
b. It was a practical and economic way to transport foods like rice from the Yangzi River valley to residents of northern regions
c. It allowed otherwise unemployed Chinese laborers to earn a living wage and support their families
d. It allowed luxury goods to move quickly to port markets on the Yellow Sea