Question

the smallest unit of life that can sustain itself is called...
an organism
a population
a community
the biosphere

Explanation:

In biology, the cell is the basic unit of life that can sustain itself, grow, reproduce, and perform metabolic functions. An organism can be made up of one or more cells. A population is a group of the same - species organisms. A community is a group of different species living in the same area. The biosphere is the global sum of all ecosystems. So the answer is based on the fundamental concept of the cell in biology.

Answer:

A. an organism