Why Are Plants That Use the CAM System of C-Fixation

Why are plants that use the CAM system of C-fixation more efficient at tolerating hot and dry climates?

A) They have no stomata. Instead they use a slower but more water efficient system of CO₂ diffusion across the epidermis for gas exchange.
B) They have evolved a system independent of phosphoenolpyruvate, the most water inefficient step in C₃ and C₄ C-fixation.
C) Their enzyme efficiency is optimal when the internal cellular environment is warmer and drier than other plants.
D) They only open their stomata at night, thus minimising transpiration loss.
E) The initial 3-carbon compound they produce in darkness is stored in the vacuole, before then being decarboxylated when light appears.