Final answer:
The second paragraph of the NOAA passage about narwhals likely describes a unique physical attribute, supporting the author's purpose by highlighting what distinguishes narwhals from other marine creatures.
Step-by-step explanation:
The correct answer to how the second paragraph of the passage of The Unicorn of the Sea by the National Oceanic and Atmospheric Administration supports the author's purpose is b. It describes a physical attribute of the narwhal that makes it unique. The purpose of the paragraph is not to relay a comic story or argue the population status of narwhals, nor to discuss the challenges in studying them, but rather to highlight what sets the narwhal apart visually or behaviorally. In this context, exhibiting a unique attribute likely refers to the narwhal's distinctive tusk, which has fascinated people and garnered attention from researchers interested in this unique cetacean species.