How did westward expansion affect Native American tribes? (5 points)

a
Railroad expansion allowed Native American hunters to sell bison meat and hides at higher rates than before.

b
Railroad expansion brought U.S. settlers in contact with bison, drastically reducing the population of this food source.

c
Westward migration of U.S. settlers increased the number of farms, causing a supplementation of bison meat with grains.

d
Westward migration of slave-owning settlers diminished the demand for bison as a beast of burden, causing the bison population to increase.