Modifications are adaptations of plant parts for specific functions. To identify a modification, we look for features characteristic of the original plant part. A) 'Eye' on potato: An 'eye' on a potato is an axillary bud, located at a node. The presence of nodes and internodes is a characteristic feature of stems. Potato tubers are modified underground stems used for storage and vegetative propagation. B) 'Scale' found in onion: Onion bulbs consist of a reduced stem base and fleshy modified leaves (scales) that store food. While the bulb includes a stem component, the 'scales' themselves are modified leaves. C) 'Tendril' found in pea: Tendrils in peas are modified leaves or leaflets used for support. D) 'Hair' present in carrot: Carrots are modified taproots. Root hairs are extensions of epidermal cells of roots, not stems. Thus, the presence of buds (eyes) on a potato directly indicates its stem nature, even though it's modified into a tuber.