Step-by-step explanation:
The volume of a simple compressible system is not fixed. At a state of equilibrium, there should be uniformity in the entire system.
From the question we have here, these are the correct options:
1. It cannot be a mixture of different substances (e.g. oxygen and nitrogent)
2. It can be composed of any phases of a substance: solid, liquid, and/or gas
3. It's state is specified if given two independent, intensive thermodynamic properties.