The correct response is:
Every cell performs all life functions.
This option is true for unicellular organisms, where one cell is responsible for all functions of life. In multicellular organisms, while cells are specialized, every cell still contributes to the overall functions of the organism. However, since the question asks for a feature common to both, the first option is the most fitting in relation to unicellular organisms. Multicellular organisms, as a whole, rely on the combination of specialized functions, but this statement also captures the essence of life function performance on a cellular level in unicellular organisms.