The correct option is
B Conserving water
Crassulacean acid metabolism, also known as CAM
photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation. These plants are able to close the stomata in the leaves during the day to reduce evapotranspiration, because they can collect carbon dioxide (CO
2) in the night and store it in the form of a four-carbon acid malate in vacuoles, and then in the daytime, the malate is transported to chloroplasts where it is converted back to CO
2, which is then used during photosysnthesis that occurs during daytime. Thus these plants are able to conserve water.