The correct answer is C: Each three-phase alternator has three separate but identical, interconnected stator windings (one for each phase) acted on by one system of rotating magnets. This is correct because in a three-phase alternator, the stator has three separate windings, one for each phase, that are interconnected. These three windings are acted upon by a single system of rotating magnets in the rotor. This configuration allows the alternator to produce a three-phase alternating current output. The other options are incorrect because they do not accurately describe the configuration of a typical three-phase alternator. Option A describes a system with three separate sets of rotating magnets, which is not the case. Options B and D describe a single-phase system, which is different from the three-phase system being discussed.