Final answer:
The characteristic that best distinguishes living things from nonliving matter is their ability to maintain homeostasis, which is the maintenance of a stable internal environment.
Step-by-step explanation:
The One Characteristic that Distinguishes Living Things
The one characteristic that best distinguishes living things from nonliving matter is the ability to maintain homeostasis. Homeostasis is the maintenance of a stable internal environment in response to fluctuations in external conditions. While all of the characteristics of life are important, homeostasis is fundamental because it underlines an organism's ability to regulate its internal environment to remain alive and functional, despite the changes outside.
Living organisms also show other key properties such as having a complex chemistry, being organized into one or more cells, the ability to grow and develop, to detect and respond to environmental stimuli, to reproduce, and to undergo evolution. Not all nonliving things can exhibit these characteristics, but it is the persistent and dynamic balance of homeostasis that truly sets living entities apart from inanimate matter.
Order, sensitivity or response to the environment, reproduction, adaptation, growth and development, regulation, and energy processing are additional traits shared by living things. When viewed collectively, these traits help define the essence of life.