(2) no. The Grand Canal was dug to strengthen the north-south traffic and consolidate the rule of the Sui Dynasty over the whole country.
(3) Difference: First, confirm the benefits of the canal. Same: wrong understanding of the disadvantages of the canal.
The four materials are all poems evaluating the Grand Canal in Sui Dynasty, and the material forms are relatively novel. We should analyze and understand the basic idea of each poem, and grasp some key words, such as "Dragon Boat", "Romantic Style" and "Yangzhou Moon", so as to get effective information.