What Is a Major Distinction Between Direct and Indirect Effects

What is a major distinction between direct and indirect effects in a community?

A) Indirect effects always include a resource such as water or light; direct effects do not.
B) Direct effects result in competitive exclusion; indirect effects do not.
C) Direct effects occur between species in different trophic levels; indirect effects include species from the same trophic level.
D) Indirect effects always include more than two species; direct effects do not.