Scientists distinguish whether an entity is living or nonliving by describing the of life.

The correct answer will be characteristic feature of life.

Explanation:

Biologists has tried to distinguish the living beings from non-living beings and developed a list of characters. These features include cellular organization, reproduction, metabolism, homeostasis, sensitivity to the environment, heredity and growth.

The first characteristic of life is cellular organisation then reproduction to produce offspring and then metabolism and others. These features are not found in the non-living material like fire, air and many others.

Thus, characteristic feature is the correct answer.

b is the best answer for this question.