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Complete Question Explanation

Assumption. The correct answer choice is (A).

Answer choice (A): This is the correct answer choice.

Answer choice (B):

Answer choice (C):

Answer choice (D):

Answer choice (E):

This explanation is still in progress. Please post any questions below!
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Why is answer choice D incorrect. The "no unknown" language confuses me.
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Well, so for this question, the "unknown" part of the answer choices, which is not explicitly referenced in the argument itself, refers to those fossils that may exist but have not yet been found by archeologists. It's basically that absence of evidence that we should rarely (if ever) take to be evidence of absence. The reason we need an answer choice to include the possibility of unknown fossil record is because we know that the earliest fossil of anthracosaurs is not older than the recent lizard fossil found to be 340 million years old. In fact, it's this piece of evidence that is used in the argument to conclude that the lizard could not have possibly evolved from anthracosaurs. However, what if we find an anthracosaur fossil that is 350 million years old? Then, we have evidence that anthracosaurs preceded the lizards, and therefore become a viable candidate as its predecessor down the evolutionary chain. This is not possible from the known evidence though, but may be possible, unless defended against by the defender assumption in answer choice A, from evidence as yet unknown, but to be discovered.

Hopefully that makes sense. Let me know if you have further questions!

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