Which one of the following is a modified stem?

Correct Option (d):

Potato is a modified underground stem, specifically a tuber. Tubers are characterized by the presence of 'eyes', which are axillary buds located at nodes. These nodes, along with internodes and rudimentary scaly leaves, confirm its stem origin. The primary function of the potato tuber is to store food, mainly starch, and to facilitate vegetative propagation.

Incorrect Options:

• (a) Carrot is a modified taproot, adapted for storing food reserves.
• (b) Sweet potato is a modified adventitious root, specialized for food storage.
• (c) Coconut is the seed of a drupe fruit. Its main stem is an upright, unbranched trunk, and it is not a modified stem for storage or other specialized functions.