Paleontologists had long supposed that the dinosaur Diplodocus browsed for high-growing vegetation such as treetop le...

SamA on January 15, 2020

Hello @tomgbean,

This is a strengthen w/necessary question, so remember that our conclusion depends entirely on this assumption. Simply strengthening the conclusion is not enough. We need to ask ourselves, "Does the argument need this to be true?"

Support: Diplodocus's bone structure would have prevented it from raising its neck.
Conclusion: Thus, Diplodocus must have fed on plants on or near the ground, or underwater.

First, we need to identify the answer choices that strengthen the argument. But then we need to decide which remaining answer choice is the necessary assumption. You were on the right track with A and C, as both strengthen the argument. However, you must proceed with the negation test. If we negate A or C, is the argument destroyed?

A. The same type of neck structure is NOT found on modern ground-feeding animals. Does this destroy the argument? No, Diplodocus could still have fed on plants on the ground. The argument does not need A to be true. Therefore it is not the necessary assumption.

C. It would be POSSIBLE for a large animal such as Diplodocus to supply blood to an elevated brain. Does this destroy the argument? No, because the limited mobility of the neck bones is still an issue. We don't care about the blood supply. Negating C does not affect the argument, therefore it is not the necessary assumption.

D. To negate, we will say that Diplodocus was able to reach high-growing vegetation by rising up on its hind legs. Does this destroy the argument? Absolutely. It makes the bone structure irrelevant. This is the only piece of support given by the argument. Without it, the conclusion falls apart. The author needs D to be true in order to draw the conclusion. This is the correct answer.