Final answer:
Five variables - internal energy, composition, pressure, temperature, and volume - can be used to specify the state of a thermodynamic system since work is path-dependent and is not a state variable.
Step-by-step explanation:
To specify the state of a thermodynamic system, one can use various thermodynamic variables. Internal energy, composition, pressure, temperature, and volume are some of these variables.
Work is not a state function; it depends on the path taken during a process, unlike the state variables which depend only on the state of the system, and so it cannot be used to specify the state of a system. Therefore, five variables among the provided list can be used to specify the state of the system: internal energy, composition, pressure, temperature, and volume.