Why Were Pastoralists Important to Settled Agriculturalists

Why were pastoralists important to settled agriculturalists?

A) They transmitted ideas,products,and people across long distances,linking villages with a wider world.
B) They left important records that influenced agricultural innovation.
C) They had so little interaction with villages that farmers came to think of them as powerful mythological beings.
D) They served as a buffer between agricultural communities and outside enemies.