The correct option is (c).
Explanation
Ecosystems are broadly classified into two categories: Natural ecosystems, which operate under natural conditions without significant human interference, and Artificial (or Human-made) ecosystems, which are created and maintained by humans.
- Pair 1 is correctly matched: A Pond is generally classified as a natural ecosystem. It is a self-sustaining freshwater (lentic) ecosystem where abiotic and biotic components interact naturally. While man-made ponds exist, in the context of ecological classification, ponds are distinct from strictly controlled environments like aquariums.
- Pair 2 is incorrectly matched: A Garden is an artificial or human-made ecosystem. It requires constant human intervention, such as watering, weeding, soil preparation, and pest control, to sustain the specific plants selected by humans.
- Pair 3 is incorrectly matched: An Estuary is a natural ecosystem found where a river meets the sea. It is a transition zone (ecotone) between freshwater and marine environments and is formed by natural geological and hydrological processes.
- Pair 4 is correctly matched: An Aquarium is a human-made ecosystem. It is an artificial enclosure where the environment (water chemistry, temperature, food supply) is entirely controlled and maintained by humans for the survival of aquatic organisms.
Key Takeaway: Natural ecosystems (e.g., forests, estuaries, ponds) are self-regulating and self-sustaining, whereas artificial ecosystems (e.g., crop fields, gardens, aquariums) lack self-regulatory mechanisms and depend on human management for stability.