I believe the best answer would be A: Community. This is because all those living things and the pond play a part for each other and in doing so they make a community.
Nutrition- microorganisms are able to feed on food materials obtained from the living or dead bodies of plants or other animals. They are therefore heterotrophs.
Movement- both localized and generalized movements which results in the animal moving from one point to another. e.g., using flagella, cilia
Excretion- they lack highly specialized excretory organs but some microorganisms use contractile vacuoles for excretion which removes waste.
