Regeneration has the effect of: a. increasing turbine speed b. increasing exhaust temperature c. cooling fluid before it enters the compressor d. preheating fluid entering the combustion chamber

d) Preheating fluid entering the combustion chamber.

Explanation:

Regeneration:

  Regeneration is a method to improve the efficiency of turbine.We know that when gases are escaping from the turbine they have high temperature and this high temperature can be used to preheat the fluid before entering to the combustion chamber. By doing this, energy input decreases as compare to without heat generation and it leads to increases the efficiency of turbine.