The correct option is A Leaf
Leaf is green, exogenous, lateral outgrowth which develops on nodes or branches of the stem, they are the flattened organs and are specialized for carrying out photosynthesis. To combat the scarcity of water in the desert and to defend grazing by the animal, leaves are modified to form spines in Opuntia. It reduces the water loss by transpiration owing to decreased surface area and also protects the plants against grazing. Opuntia has very small and deciduous spines with many barbs along its length which are also termed as glochidium as well as the fixed spines.
Thus, the correct answer is option A.