ecology is one component of environmental science that studies organismal

Your answer to fill in the blank should be "interactions"

Interactions Ecology is one component of Environmental Science that studies organismal interactions. Ecology is a subfield of biology which deals with living things and how they react and interrelate with one another. Organismic interactions has many aspects to consider such as mutualism (two organisms that benefits each other’s behavior), prey-predator (an organism eats the other weaker organisms), parasitism (the opposite of mutualism), and exploitation (decaying). These types of organismic relationships are only within these interactional creatures which either serves to be allies or enemies, for short.     

Your answer is d.all of the above! hope this ! : )