I think the answer to this is letter B
Answer:
Hope this helps
Explanation:
1 The fish could have been overfished so they were all taken
2 when thd dump was built the river got polluted and killed the fish
3 a mix of both so the fish decided to leave.
Those are the reasons I belive hope this helps.
The Silk Road was the easiest way for people to trade supplies but over the years people started to taxes everything in the silk road to the point no one wanted to do any trading there