The correct option is
C cellular level
The living world (where we live) is diverse and complex and can be understood at various levels of biological organisation.
Cells form the basic structural and functional unit of every organism. These cells are made up of different biomolecules which organise themselves to form organelles present in the cell. The organelles work together to form a functional unit called a cell. There are organisms which are made up of a single cell like Amoeba. But most of the organism are made up of millions of cells. This is the cellular level of organisation. Hence option c is correct.
A group of similar cells, performing the same function, combine to form tissues. There are different types of tissues present in organisms like nervous tissue, muscular tissue, etc. This is called tissue level of organisation.
Different tissues combine to form organs (brain and spinal cord) and organs combine to form an organ system (nervous system). Various organ systems together form an organism. An organism is the highest level of organisation. Example - Human being.
Similar organisms that are capable of breeding amongst themselves are further organised into species. Example - Human species.
Members of the same species in an area organise themselves into groups called populations (Human population in Bangalore) and populations of different species build communities. For example, a farmer community with cattles (cows, buffaloes) in an area.
The entire living/biotic community of an area along with the abiotic components in it, form an ecosystem. For example, living (fishes, frogs) and nonliving things (soil, temperature) in a pond ecosystem.