The correct answer is D) reduce eddy current losses. The armature cores of DC motors are constructed with laminated steel sheets to reduce eddy current losses. Eddy currents are induced electrical currents that circulate within the core material, causing energy losses and heating. By using laminated steel sheets instead of a solid core, the paths for these eddy currents are broken, minimizing the losses and improving the efficiency of the motor. The other options are incorrect because: A) Lamination does not directly eliminate hysteresis losses, which are caused by the changing magnetic fields within the core material. B) Lamination does not directly affect brush sparking, which is more dependent on the design of the commutator and brushes. C) Lamination does not compensate for armature reaction, which is a magnetic effect caused by the armature current interacting with the main field.