Welcome! You are encouraged to register with the site and login (for free). When you register, you support the site and your question history is saved.
Review: Bird Navigation I
Explanation
The answer to this question is almost certain to appear in
the second paragraph, where the beak theory is summarized. Anything mentioned
later is out, which rules out wandering macrophages in (A), cluster N in (D),
and grains outside of the beak in (E). The trigimenal
nerve is evidence for the theory, not the substance of the theory. The
substance is the magnetite grains. Choice (B) doesn't use the word "magnetite,"
but it's the only possible option.
The correct answer is (B).
If you believe you have found an error in this question or explanation, please contact us and include the question title or URL in your message.