Over time, tensions arose between the owners of the railroads and Western farmers and ranchers over the issue of 1. Train schedules.
2. Transporting goods back West.
3. Building new railroads.
4. High shipping costs.

d is the correct answer.

b is incorrect because it makes food by itself

c is incorrect because us humans don't know how to produce their own food using the sun like plants.

a is incorrect because consumers can depend on carnivores for eating food for consumers to eat the dead organism. same thing with omnivores.

its d i know cause i've been googling it

answer; the federal reserve system;