In c3 plants the conservation of water promotes
a. photosynthesis
b. a shift to c4 photosynthesis
c. the opening of stomata
d. photorespiration
e. the light reactions

The correct option is d. In C3 plants the conservation of water promotes photorespiration.

Explanation:

Photorespiration is a metabolic pathway that leads to the loss of half the carbon fixed by photosynthesis, it occurs when the rubisco enzyme (which is responsible for carrying out the carbon fixation) of the Calvin cycle acts on oxygen instead of dioxide carbon. Photorespiration occurs in C3 plants, (considered C3, by the three carbon compound) when the CO2 concentration is reduced. The first step of the Calvin cycle is the fixation of carbon dioxide by rubisco, but at low concentrations of CO2, oxygen begins to be set in place. In conditions of moderate temperatures when C3 plants have enough water, the carbon dioxide supply is abundant and photorespiration is not a problem.  

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.