The correct answer is D. all above methods.
The internal resistance of a cell is the resistance to the flow of current through the cell. It is caused by the resistance of the electrolyte, the resistance of the electrodes, and the contact resistance between the electrodes and the electrolyte.
The internal resistance of a cell can be reduced by increasing the plate area, putting the plates very close together, and using a vent plug to permit gas formed during discharge.
Increasing the plate area increases the surface area of the electrodes, which allows more current to flow through the cell. Putting the plates very close together reduces the distance that current has to travel, which also reduces the internal resistance. Using a vent plug allows gas to escape from the cell, which prevents the build-up of pressure and reduces the internal resistance.
All of these methods can be used to reduce the internal resistance of a cell and improve its performance.