The correct answer is B) Squirrel-cage. In the split-phase family of single-phase motors, the most commonly used rotor type is the squirrel-cage rotor. This is because the split-phase motor design uses a starting winding and a running winding to provide the necessary starting torque, and the simple and robust squirrel-cage rotor is well-suited to work with this type of motor configuration. The other options are not commonly used in split-phase single-phase motors. Drum rotors are typically found in DC motors, salient pole rotors are more common in polyphase AC motors, and wound-rotors are typically used in larger, more specialized AC motor designs.