Closing of stomata can be both useful and harmful for a plant. What is the correct reason?

Correct answer: It reduces water loss but can also reduce carbon dioxide entry

Stomata are pores that regulate exchange between the leaf and the atmosphere. When they close, diffusion of water vapour out of the leaf decreases, which helps prevent excessive water loss during dry conditions. However, carbon dioxide also enters mainly through these pores, so closure can limit photosynthesis and food production. Thus option A correctly gives both effects; the other options describe unrelated or impossible functions.