3. D. A deer decomposing in the soil provides food for bacteria and nutrients for plants to grow.
4. A. All ecosystems are home to living beings that interact with each other.
Explanation:
In an ecosystem, different organisms interact with each other because one organism is the food of another organism or in other words organisms interact with each other in order to take nutrients from one another. There are some interaction in which both gets benefit and some interaction only one get benefit and the other get harmed. Examples of such type of interaction are Predation, parasitism and herbivory.
