The correct option is
C A community
A. An ecosystem is stable, settled unit of nature consisting of a community of organisms interacting with each other and with their surrounding physical and chemical environment.
B. A habitat is a place where an organism lives and represents a particular set of environmental conditions suitable for its successful growth.
C. A community is a group of populations of different species in a given area.
D. Species is a group of individuals which resemble each other in morphological, physiological, biochemical and behavioural characters.
E. The planet Earth along with its atmosphere (air, land and water) that sustain life is called biosphere.
Hence, Different populations of organisms livng together in a given area are called community.
So, the correct answer is 'A community'.