Answer:
A. a decreased rate of photosynthesis.
Explanation:
Stomata is a structure in the leaves of higher plants, which they use majorly for the purpose of gas exchange. However, the process whereby plant loses water called transpiration also occurs via the stomata. In a situation whereby the availability of water in a plant's environment is low, the plant responds by closing its stomata in order to conserve water (reduce the amount of water that the plant loses through its leaves due to transpiration).
Closing the stomata by plants means not allowing ample carbon dioxide (CO2), which is needed for the process of photosynthesis to occur, to enter the plant. This will most likely result in a DECREASED RATE OF PHOTOSYNTHESIS.