In a two-stage flash evaporator, the sea water feed temperature is increased as it passes through the __________.

Correct Answer: Option D — all of the above

In a multi-stage flash evaporator, the feed water is preheated as it passes through the distilling condensers of each stage. This heat recovery process utilizes the latent heat released during condensation to raise the temperature of the incoming seawater, significantly improving the thermal efficiency of the plant.