The distinguishing characteristic of a synchronous motor is that it runs ____________ the rotating magnetic field.

A synchronous motor is designed to operate at a speed that is synchronized with the rotating magnetic field produced by the stator. This means that the rotor of the motor rotates at the same frequency as the magnetic field, hence the term "synchronous."

This characteristic allows synchronous motors to achieve higher efficiency and better speed regulation compared to other types of motors. The ability to maintain this synchronous relationship provides advantages in applications where precise speed control is essential.

In contrast, other options would imply behaviors that are characteristic of different types of motors. For example, running "in reverse" or "out of sync" would apply to systems where the rotor does not maintain a constant phase relationship with the magnetic field, which is not the case for synchronous motors. Similarly, the idea of running "slower than" the magnetic field doesn't apply because, by definition, a synchronous motor operates at the same speed as the magnetic field. Therefore, the best description of a synchronous motor is that it runs in step with the rotating magnetic field.