The correct answer is: D. reduce eddy current loss.
Eddy currents are induced currents that flow in a conducting material when it is placed in a changing magnetic field. These currents can cause significant losses in a generator, as they dissipate energy as heat. Laminating the armature of a generator helps to reduce eddy current losses by breaking up the conducting material into thin sheets. This reduces the size of the loops that the eddy currents can flow in, and therefore reduces the amount of energy that is lost.
The other options are incorrect. Option A is incorrect because lamination does not reduce the bulk of the armature. Option B is incorrect because lamination does not provide the bulk of the armature. Option C is incorrect because lamination does not insulate the core.