The factor that most seriously limits the value of grades for certification is that grade:

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.

answer; implicit memories explicit;

answer; the intervening variable;

answer; /// working class;