Solution

•Stem horns- Sometimes thorns are present in the axil of the leaves or apex of stem. These are modified stem that perform the function of either climbing or defense. For example, Citrus.
•Phylloclades- These are the modified stems that perform the function of leaves as they are green and photosynthetic. Formation of phylloclades help the plants to grow in dry and xerophytic habitats because transpiration is very much reduced from these phylloclades. For example, Opuntia.
•Cladodes- These are green photosynthetic stems that are generally one internode long. These develop by the modification of only stem branches of limited growth and are photosynthetic. The true leaves of the plants are reduced to scales or spines. For example, Asparagus.
Hence, the correct match is A- 3, B- 2, C- 1