Mountain Men young American trappers and traders in the Rocky Mountains.
Option(b);
Step-by-step explanation:
- Mountain men were a group of explorers who discovered the new immigrant trails that led to new territories. 
- These inventions result in the motivation for trade and other commerce opportunities. 
- They improved roads that allowed free movement of wagons that enables the Americans to settle in the West. 
- Also, they organized wagons to facilitate easy transportation. 
- Their main source of trade was fur which initially gave rise to their trade operation and functions that introduced new dealings lasted for nearly three decades.