Final answer:
In a eudicot embryo, the stem originates from the Plumule (option D), which is part of the epicotyl. The hypocotyl is the region that forms the stem, while the radicle develops into the root system.
Step-by-step explanation:
In a eudicot embryo, the stem comes from the Plumule. Specifically, the hypocotyl is the region of the embryo that forms the stem after germination. The radicle gives rise to the root system, while the cotyledons serve as the first leaves of the young plant and as a source of nutrients until the plant is capable of photosynthesis. The Plumule is part of the epicotyl and is responsible for forming the leaves and the shoot apical meristem. Upon germination, the epicotyl, which protects the plumule, grows upwards and once it reaches the soil surface, the hook straightens, allowing the plumule to develop into the stem and leaves.