The correct option is
B Conserving water
Certain plants especially succulents which grow under extremely xerophytic conditions, fix atmospheric carbon dioxide in the dark. Since the process was first observed in the plants belonging to family Crassulaceae such as
Bryophyllum, Kalanchoe, Sedum etc., it was termed crassulacean acid metabolism (CAM). Such plants are known as CAM plants. The most characteristic feature of these plants is that their stomata remain open at night but closed during the day. Thus, CAM is a kind of adaptation in succulents to carry out photosynthesis without much loss of water. This helps in conserving water in these plants.
Thus, the correct answer is option B.