Final answer:
The spinning turbine (c) is a source of mechanical energy that can be used in the construction of a generator.
Step-by-step explanation:
The source of mechanical energy that can be used in the construction of a generator is the spinning turbine (c). A turbine is a device that converts the kinetic energy of a flowing fluid (such as steam, water, or wind) into rotational mechanical energy. This rotational mechanical energy is then used to rotate a wire coil within the generator and generate electricity.