Technician a says that that both slip rings must be insulated from the rotor shaft. technician b says that at least one slip ring must be grounded to the shaft to provide a complete circuit for current flow

Technician A is correct while Technician B is incorrect.

Explanation:

If Technician a says that that both slip rings must be insulated from the rotor shaft, then, technician a is correct.

If technician b says that at least one slip ring must be grounded to the shaft to provide a complete circuit for current flow, this statement is incorrect because each slip ring must be connected to one of the three phases of rotor windings. And the slip ring brushes are connected to a resistive device ( like a rheostat). When the slip rings turn with the rotor, the brushes will maintain constant contact with the rings and transfer the resistance to the rotor windings. Therefore, Technician A is correct while Technician B is incorrect.

28. evolution

29. environment, survive, offspring  

explanation: