Of all excavation hazards, poses the greatest risk.
a. a cave-in
b. inhalation
c. moving machinery

a is the answer because it just is

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.