Passage Summary: A crab living in the pitch-black deep sea can see UV light; because there is no sun there, the author assumes it uses this vision to find and eat glowing creatures.

Conclusion: The deep-sea crab likely hunts bioluminescent prey.

Reasoning: The crab has eyes sensitive to ultraviolet light at depths where sunlight cannot reach, and since the crab is not bioluminescent itself, its UV vision is likely an adaptation for detecting other glowing organisms.

Analysis: To weaken this argument, we need to find an alternative explanation for why the crab has UV-sensitive eyes or why it might not be hunting. The author assumes that if the crab can see light in the dark, it must be using that light to find food. Perhaps the UV sensitivity is used to avoid predators rather than catch prey, or maybe it is a vestigial trait from ancestors that lived closer to the surface. Look for an answer choice that breaks the link between 'seeing UV light' and 'hunting prey.'