Final answer:
CAM plants fix carbon mostly at night by opening their stomata and store it as organic acid for sugar synthesis during the day. They have adapted to grow slowly due to their low photosynthetic rates.
Step-by-step explanation:
CAM plants, also known as Crassulacean Acid Metabolism plants, have unique adaptations to conserve water in desert environments. They fix carbon mostly during the night by opening their stomata at that time, allowing them to take in CO2. This CO2 is then stored as an organic acid, such as malic acid, and can be used during the day for sugar synthesis. CAM plants grow slowly due to their low photosynthetic rates. Therefore, the correct answer is D. open stomata only at night C. grow slowly.