In both cases, rubisco is not used to fix carbon initially (Ans C)
Photosynthesis is similar in C4 plants and CAM plants because they separate the light and dark reactions to reduce photorespiration. Plants which lives in dry and hot condition may be C4 plants and CAM plants have an alternative method of carbon fixation.
In C4 plants carbon dioxide is taken into the leaves through the stomata present in leaves but is converted to a 4 carbon molecule, then this molecule can be pumped to the deeper layer present on the leaves for the Calvin cycle to occur away from the presence of the oxygen.
CAM plants take in carbon dioxide at night time and convert them to other carbon molecules which can be stored in the vacuole. During the day time, CAM plants shut their stomata and instead utilize the carbon which was brought at night to reduce water loss and photorespiration.
During photorespiration plants shut their stomata and reduce the intake of CO2 and reduce water loss, with a limited amount of CO2, rubisco uses oxygen instead of CO2 in the dark reaction. (which is present in both C4 and CAM plants)