Answer:
They blazed trails used by later settlers.
They built trading relationships with American Indians.
They established trading posts that grew into towns.
Explanation:
The role that trappers and traders play in opening up the West is best displayed in options first, second, and fourth. These options clearly exemplify the part portrayed by trappers and traders by stating that how they blazed trails used by last settlers and how they built trading affiliations with American Indians and how well they could establish trading posts that grew into towns. Thus, the options that apply are A, B, and D
