Bulbil is a modification of
A. Underground stem
B. Bases of leaves
C. Buds
D. Radicle

Hint: Aerial stem modifications are modifications to the aerial stems, vegetative buds, and floral buds of plants growing in different conditions and which perform functions such as climbing, protection, synthesis of food, or vegetative propagation. Aerial stem structures that undergo modifications to perform these special functions include tendrils, thorns, hooks, phylloclade, tuberous stems, and bulbils.

Step by step answer:When the axillary bud becomes fleshy and rounded due to storage of food, it is called bulbil. It gets detached from the plant, falls on the ground, and develops into a new plant. e.g. Dioscorea. It is in an axel (the space between leaf and stem).
It is a small, young plant that is reproduced vegetatively from axillary buds on the parent plant's stem or in place of a flower on an inflorescence.
These young plants are clones of the parent plant that produced them—they have identical genetic material. The formation of bulbils is a form of asexual reproduction, as they can eventually go on to form new stand-alone plants.
Hence option C is correct.

Note: A bulbil is also referred to as bulbel, bulblet, or pup. All bulbils produced by bulbous plants are to be considered bulbs, but not all bulbils are to be considered bulbs. For example, non-bulbous plant groups, like various genera within the subfamily Agavoideae, are well known to produce bulbils that do not actually meet the botanical criterion to be considered a bulb. Bulbil helps in vegetative reproduction.