What is the main difference between C3 and C4 carbon fixation? a. In C3 carbon fixation, plant stomata are open during the day, while they are open at night for C4 carbon fixation. b. C3 processes take place throughout the leaf, while C4 processes take place in the inner cells. c. C3 carbon fixation is more common in areas with high light intensity than C4 carbon fixation. d. C3 processes are more efficient than C4 processes in high temperatures.