Question

how did the physical features of east asia affect the route of the silk road?
the rough terrain blocked its extension into eastern lands.
the seas kept it from connecting with northern lands.
the river systems blocked passage along the trade routes.
the mountains forced it to follow a central route.

Explanation:

The mountains in East - Asia, such as the Himalayas, created natural barriers. Traders had to find a route that avoided the most difficult mountainous areas, which led to the Silk Road following a more central route through relatively more passable terrain. The rough terrain of mountains made it difficult to deviate into other directions. Seas were not relevant to the north - south extension of the Silk Road in this context, and river systems did not primarily block the passage as much as the mountains did. The rough terrain mainly in the form of mountains affected the route.

Answer:

The mountains forced it to follow a central route.