Question

every living thing within an ecosystem is...
interconnected.
a keystone species.
an invasive species
isolated.

Explanation:

In an ecosystem, living things interact through food webs, nutrient cycles, and other ecological processes. "Interconnected" reflects this interdependence. A keystone species is a specific type (not all organisms), invasive species are non - native and disruptive (not all organisms), and "isolated" contradicts ecological interactions.

Answer:

A. interconnected.