(1) According to the information in the picture, most parts of the United States are located in the north temperate zone, and there is no tropical zone in China, so it is impossible to grow tropical crops, and it is necessary to import a large number of tropical agricultural products such as coffee, cocoa and natural rubber;

(2) The Mississippi River flows into the Gulf of Mexico from north to south, so it is judged that the terrain in the central part of the United States is high in the north and low in the south;

(3) Because the terrain in the middle of the United States is plain, the cold air from the Arctic Ocean south and the warm air from the Gulf of Mexico north directly drive the middle of the United States.

So the answer is: (1) north temperature; Coffee; Cocoa; (2) high in the north and low in the south; (3) dull.