Concept: An ecosystem's stability is its ability to resist change and recover from disturbances. Marine ecosystems have vast size, constant temperature, and slow nutrient cycles, making them the most stable.
Explanation: Marine (ocean) ecosystems cover about 71% of Earth's surface.
They experience minimal temperature fluctuations compared to land ecosystems.
The deep ocean has very stable conditions: no seasons, constant pressure, and low light.
Marine food webs are complex and have remained relatively unchanged for millions of years, even through major climate shifts.
In contrast, forests, mountains, and deserts face frequent changes like fires, droughts, storms, and temperature extremes.
Thus, marine ecosystems are the most stable.
Answer: A. Marine (ocean)