Dinosaur expert: Some paleontologists have claimed that birds are descendants of a group of dinosaurs called drome...

on January 6, 2021

Dinosaur expert

Please can you explain why the answer here is D, rather than C? Many thanks!

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Shunhe on January 9, 2021

Hi @Anna2020,

Thanks for the question! So this is a strengthen with necessary premise question. The conclusion is going to be the last sentence of the stimulus. And the reason for believing this is that there are older bird fossils than the oldest dromeosaur fossils. Remember, we can use the negation test to test out answer choices.

(D) says that the argument assumes that known fossils indicate origin dates of both species. Well, let’s use the negation test. Let’s say they don’t indicate the origin dates. Then why do we care about the fossils at all? That would completely destroy the argument, and so (D) is the necessary assumption.

(C), on the other hand, says that knowledge of the fossils is complete. But this assumption is too strong. We don’t need to know that the knowledge is complete—every single little detail about the fossils. We don’t even necessarily have to have a complete fossil. We just need to know when the oldest fossils are. And so (C) is too strong of an assumption and not necessary, making it wrong.

Hope this helps! Feel free to ask any other questions that you might have.