Pretty sure its d... hope this helps
“No man is an island.”This saying is also true for organisms in an ecosystem. No organism exists in isolation. Individual organisms live together in an ecosystem and depend on one another. In fact, they have many different types of interactions with each other, and many of these interactions are critical for their survival.
Mainly to make life easier.
if one layer changes than scientists don't need to change all of their data.
it also helps keep organized.
hope this helped
ebs02
:)