Answer and Explanation:
According to the paragraph, "Hueter believes the teeth are vestigial, an evolutionary leftover from the whale shark's ancestor." This explains why the whale shark does not bite or chew. A vestigial structure or organ is an anatomical feature that remains even though it no longer has use for the more evolved creature. An example of vestigial organ in humans is the appendix. In the case of the whale shark, the teeth are vestigial structures - they no longer function, but have remained as a leftover of evolution. That is why the whale shark cannot use them to bite or chew.
I lean more towards (A) because the husband is talking to his wife as a child and not as an adult which tends to describe and condescending attitude. However you could make an argument for (F).
