The following responses apply to how mountains and high plateaus influenced the rise and growth of empires in mainland Southeast Asia:
- Mountains and high plateaus made it difficult for the rest of Asia to trade with and conquer mainland Southeast Asia.
- Mountains and high plateaus protected the regional empires that included the four main river valleys of Southeast Asia.
- Mountains and high plateaus encouraged cultural diffusion in the empires that arose in mainland Southeast Asia.
The first option you provided is incorrect as mountains and high plateaus did not necessarily prevent civilizations from developing along the river valleys; in fact, the river valleys often served as focal points for agricultural civilization.