Step 1: Understanding the Concept:
This question is a critical appreciation of the poet John Keats and asks to identify the central principle he explores in his nature poetry.
Step 2: Detailed Explanation:
John Keats is one of the foremost poets of the Romantic movement. A central theme and driving force in his work is the celebration and exploration of beauty in all its forms—in art, in nature, and in human experience. His poems are renowned for their rich sensory imagery ("memorable pictures") that capture the beauty of the natural world. His famous line from "Endymion", "A thing of beauty is a joy for ever," encapsulates his philosophy. Therefore, the principle he consistently exhibits in nature is beauty.
Step 3: Final Answer:
The core principle that John Keats exhibits in his depiction of nature is beauty. Therefore, option (B) is the correct answer.