Correct option (a) Open during the night and close during the day
Explanation :
CAM (Crassulacean Acid Metabolism) plants open stomata only at night (when temperature is low and humidity is high) to cause lesser loss of water (e.g. Agave, Opuntia, etc.). So, CAM photosynthesis is a carbon fixation pathway that evolved in some plants as an adaptation to add condition.