An ecosystem is a geographical area
where plants, animals, landscape, and climate all interact
where plants, animals, landscape, and climate are independent of each other
where plants and animals interact together
where organisms interact with each other

The answer is where plants, animals, landscape, and climate all interact.

An ecosystem involves interactions of living things with nonliving things in their environment, interactions of biotic and abiotic factors. So, biotic factors are plants, animals, and other organisms, and abiotic factors include landscape, climate, and other. Their interaction in a geographical area means ecosystem.