The correct answer is D. 100 thousand volts.
A color television set using a picture tube has a high voltage used to accelerate electron beams to light the screen. This voltage is about 100 thousand volts. This high voltage is necessary to accelerate the electrons to a high enough speed so that they can hit the phosphors on the screen with enough energy to cause them to emit light.
The other options are incorrect. Option A, 500 volts, is too low a voltage to accelerate electrons to a high enough speed to cause the phosphors to emit light. Option B, 5 thousand volts, is a bit closer, but it is still not high enough. Option C, 25 thousand volts, is closer still, but it is still not quite high enough. The only option that is high enough is option D, 100 thousand volts.