Step 1: Understanding the Question:
This question tests knowledge of the useful parts of medicinal plants.
Step 2: Detailed Explanation:
Plantago ovata (Psyllium) is cultivated for its seed husk (C).
The seed husk is used as a dietary fiber (Isabgol).
Root (A), Shoot (B), and Leaves (D) are not the useful parts.
Thus, the useful part is seed husk only.
Step 3: Final Answer:
Thus, the useful part of Plantago is seed husk, which corresponds to option (A).
[0.5cm]