Explanation:

Ocean

Oceans are the most stable ecosystems. Other terrestrial ecosystems undergo changes and succession of biotic components. But oceans remain stable for the long duration of time. Mountains, deserts and forests are created and destroyed by various natural geological and anthropogenic factors but oceans have remained stable throughout the Earth's long history. Their volume is huge and hence, small changes are not easily felt in oceans. Therefore, the correct answer is option D.