Indo-China Peninsula is named because it is located in the south of China. The northern part of Indochina Peninsula is high and steep, which is connected with the mountains and rivers of China. Mountains and rivers extend from north to south, forming a surface pattern of alternating mountains and rivers. The upper reaches of rivers in Indo-China Peninsula are among the mountains, and are rich in hydraulic resources. After entering the downstream, the water flow is gentle and sediment is deposited, forming an alluvial plain. These plains are low-lying and are important agricultural areas in Southeast Asia.
So choose: a.