Which one of the following is a xerophytic plant in which the stem is modified into a flat, green and succulent structure?

Opuntia is a xerophyte, generally found growing on the hill slopes in dry sunny areas. It is adapted to rapid absorption and storage of water from the infrequent rains of the dry regions. The plant is covered with a thick cuticle which retards transpiration to a considerable extent. In this plant, the leaves are modified into spines, whereas the stem is modified into flat, spongy, leaf-like structures, with the water-storage tissues inside them. It is a succulent shrub, growing under desert and dry conditions; the stem and branches are green, and become flattened and look very much like leaves are called as phylloclades. Thus, the correct answer is option B.