The correct answer is: A. reduce hysteresis loss.
A transformer core is laminated to reduce hysteresis loss. Hysteresis loss is the energy lost in a magnetic material when it is repeatedly magnetized and demagnetized. The laminations are thin sheets of steel that are insulated from each other. This insulation prevents the eddy currents from flowing from one sheet to another, which reduces the hysteresis loss.
Eddy current losses are also reduced by lamination, but they are not the primary reason for laminating a transformer core. Eddy current losses are caused by the movement of electric current in a conductor. The current creates a magnetic field, and this magnetic field interacts with the magnetic field of the transformer core. This interaction causes the current to flow in a circular path, which is called an eddy current. Eddy currents cause heat to be generated, which reduces the efficiency of the transformer.
Copper losses are caused by the resistance of the copper wires in the transformer. The resistance of the copper wires causes a voltage drop, which reduces the amount of power that is transferred to the load. Copper losses can be reduced by using thicker wires, but this increases the cost of the transformer.
In conclusion, a transformer core is laminated to reduce hysteresis loss. Eddy current losses are also reduced by lamination, but they are not the primary reason for laminating a transformer core.