The correct answer is: D. All of the above.
The corona discharge is a form of electrical discharge that occurs when an electric field is applied to a conductor. The discharge is caused by the ionization of air molecules near the conductor, and it can be seen as a bluish glow. The corona discharge is affected by the size, shape, and surface condition of the conductor.
The size of the conductor affects the corona discharge because it determines the electric field strength at the surface of the conductor. The higher the electric field strength, the more likely it is that air molecules will be ionized.
The shape of the conductor also affects the corona discharge. A sharp point on a conductor will have a higher electric field strength than a blunt point, and it is therefore more likely to cause a corona discharge.
The surface condition of the conductor also affects the corona discharge. A conductor with a rough surface will have a higher electric field strength than a conductor with a smooth surface, and it is therefore more likely to cause a corona discharge.
The corona discharge can be a problem in high-voltage equipment, because it can cause power loss and equipment damage. It can also be a nuisance, because it can cause radio interference and light pollution.