Why Was the Construction of the Grand Canal Necessary

Why was the construction of the Grand Canal necessary?

A) Major river systems in China ran from north to south, and the canal was necessary to connect the coastal regions with the western frontier.
B) Chinese population was increasingly concentrated along the northern plains along the Yangzi River.
C) The Yangzi River valley was becoming the major food-producing region of China by the late Tang era.
D) The canal connected the Tang capitals of southern China, Changan and Loyang, with the newly acquired regions in the north.