China's three major plains are the Northeast Plain, the North China Plain, and the Yangtze River Middle and Lower Reaches Plain. Plains are areas on land with relatively low altitudes. Plains are the flattest areas on land, with an altitude of generally below 200 meters. Plains are broad and flat with small undulations. They are distinguished from hills by their small undulations and from plateaus by their small heights. There are many types of plains, which can generally be divided into tectonic plains, erosion plains, and accumulation plains according to their causes, but most of them are generally formed as a result of river impact. Accumulation plains are plains formed by compensatory accumulation of sediments during the process of slow crustal movement. Alluvial plains, floodplains, and marine plains are all accumulation plains. For example, the Yangtze River Middle and Lower Reaches Plain is an alluvial plain. Erosion plains, also called denudation plains, are stone plains formed when the weathered materials are gradually denuded due to gravity and the action of flowing water under the condition of long-term stability of the crust. Erosion plains are generally slightly undulating, such as the plains in Xuzhou, Jiangsu Province, my country. Tectonic plains are plains formed by crustal uplift or sea level drop, such as the Russian plains. The total area of ​​plains in the world accounts for about one-fourth of the total land area of ​​the world. Plains are not only vast, but also fertile, with dense water networks and developed transportation. They are places where economic and cultural development was early and rapid. The middle and lower reaches of the Yangtze River in my country are known as the "land of fish and rice". Other important mineral resources, such as coal and oil, are also concentrated in the plains. ■Middle and Lower Yangtze Plains The middle and lower reaches of the Yangtze River in China are strip plains along the coast east of the Three Gorges of the Yangtze River. It is bounded by the Huaiyang Hills and the Huanghuai Plain in the north and the Jiangnan Hills and the Zhejiang-Fujian Hills in the south. It is formed by alluvial deposits from the Yangtze River and its tributaries. It covers an area of ​​about 200,000 square kilometers. The terrain is low and the altitude is mostly about 50 meters. The middle reaches of the plains include the Jianghan Plain in Hubei, the Dongting Lake Plain in Hunan (collectively known as the Two Lakes Plain), and the Poyang Lake Plain in Jiangxi; the lower reaches of the plains include the Yangtze River coastal plains and Chaohu Plain (Central Anhui Plain) in Anhui, as well as the Yangtze River Delta between Jiangsu, Zhejiang, and Shanghai. Most of the climate belongs to the northern subtropical zone, and a small part belongs to the northern edge of the mid-subtropical zone. The average temperature is 14-18℃, the average temperature of the coldest month is 0-5.5℃, the absolute minimum temperature is -10--20℃, the average temperature of the hottest month is 27-28℃, and the frost-free period is 210-270 days. Agriculture has two or three crops a year, and the annual precipitation is 1000-1400 mm, concentrated in spring and summer. Zonal soil is only found in low hills and gentle slopes, mainly yellow-brown soil or yellow-brown soil. The southern edge is red soil, and most of the plains are paddy soil. Agriculture is developed, and the land reclamation index is high (62.1% in Shanghai and 45.6% in Jiangsu). It is an important grain, cotton and oil production base. It is rich in rice, wheat, Cotton, rapeseed, silkworms, ramie, jute, etc. The rivers and lakes are crisscrossed, and the lake area is 20,000 square kilometers, which is equivalent to 10% of the plain area. There are more than 1,300 large lakes in the Two Lakes Plain, including more than 10,000 small lakes, with an area of ​​more than 12,000 square kilometers, accounting for more than 20% of the Two Lakes Plain. It is the place with the most lakes in China. There are large freshwater lakes such as Poyang Lake, Dongting Lake, Taihu Lake, Hongze Lake, Chaohu Lake, etc., which are connected to the Yangtze River. They have the function of natural reservoirs to regulate water volume and reduce flood peaks. They produce fish, shrimp, crabs, lotus, water chestnuts, reeds, and Chinese The world's treasures such as the Chinese sturgeon, the Yangtze alligator, and the Baiji dolphin, aquatic products play an important role in China, and it is known as the land of fish and rice. It is one of the most economically developed regions, with cities such as Shanghai, Nanjing, Wuhan, Nanchang, Suzhou, Wuxi, Changzhou, Nantong, Wuhu, and Changsha. The main industries include steel, machinery, electricity, textiles, and chemicals, and it is an important industrial base. The plain is the hub of China's north-south and east-west transportation networks, and both water and land transportation are very developed. The Yangtze River runs through the middle of the country, becoming an east-west water transport artery, and its countless tributaries form a huge waterway network. The world's ten largest plains (1) Amazon Plain in South America: 5.6 million square kilometers (2) Eastern European Plain in Europe: 4 million square kilometers (3) West Siberian Plain in Asia: 2.6 million square kilometers (4) La Plata Plain in South America: 1.5 million square kilometers (5) Great Plains in North America: 1.5 million square kilometers (6) Turan Plain in Asia: 1.5 million square kilometers (7) Gangetic Plain in Asia: 450,000 square kilometers (8) Indus Plain in Asia: 300,000 square kilometers (9) Central European Plain in Europe: 300,000 square kilometers (10) Songliao Plain in Asia: 250,000 square kilometers