Which of the following materials is used in the manufacture of resistance grids to be used in the starters of largemotors ?

The correct answer is A. Copper.

Copper is a good conductor of electricity, which is necessary for resistance grids. It is also a strong material that can withstand the heat generated by the resistance grid.

Aluminium is also a good conductor of electricity, but it is not as strong as copper. Steel is not a good conductor of electricity, and cast-iron is not a good conductor of electricity or strong enough to withstand the heat generated by the resistance grid.

Therefore, copper is the best material for the manufacture of resistance grids to be used in the starters of large motors.