Which statements describe ecosystems?

balance is required for the survival of an ecosystem.
healthy ecosystems can support an unlimited number of plant and animal species.
one way to determine an ecosystem's health is by its biodiversity.
the parts of an ecosystem are independent and have little to do with each other.
people's actions sometimes improve the health of an ecosystem.
predators play a role in balancing the earth's ecosystems.

Ecosystem refers to a community consisted of all the living organisms (biotic component), their surroundings (abiotic component), and their interaction with each other as well as with abiotic component in a given area.

The two components (biotic and abiotic) of an ecosystem are mainly connected through energy flows and nutrient cycles.

The energy flows and nutrient cycles help in maintaining the balance within biotic, abiotic, and between biotic and abiotic components. It is very important for the survival of an ecosystem.  

For example, disturbed carbon cycle can affect the whole ecosystem.

Both biotic (including human beings) and abiotic components can affect the ecosystem in positive as well as negative manner.

Predation is a biological interaction which also helps in maintaining the balance in an ecosystem. It does so by limiting the number of organisms present at lower trophic levels.

A healthy ecosystem is able to a large number of plants and animal but not unlimited number due to the limitations of resources and trophic levels.

An ecosystem with high biodiversity often considered as healthy ecosystems as they are more stable, more productive, and supports a large number of animal and plant lives.

Thus, the correct statements would be:

c. movement because i took the test and it lets me review my answers

the answer to your question is:

c. complementary base-pairing