Official Explanation

Argument Construction

This question requires that we identify the answer choice that lends the most support for the scientists' conclusion. This conclusion states that the islands of Marlandia must not have been completely submerged during a global rise in sea level as had previously been thought.

Scientists arrived at this conclusion after being surprised to find that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. They had believed that this prehistoric species had become extinct millions of years ago when Marlandia was submerged due to a global rise in sea level.

What are some ways that we can strengthen support for the conclusion? Information that rules out the possibility that the reptile could have survived even if the islands had been completely submerged would strengthen support. So would information that rules out the possibility that the reptile had migrated to somewhere other than Marlandia but traveled back to Marlandia after the islands were no longer submerged.

A. Even if it is true that reptiles on Marlandia have adapted to environmental changes since the sea-level increase, that does not support the belief that part of Marlandia never became submerged when the sea level rose. It does not rule out either of the two alternative explanations discussed immediately above, for instance.

B. The argument's conclusion is about whether some part of Marlandia never became submerged. Information indicating that Marlandia separated from a much larger landmass many millions of years before the global sea-level rise is not relevant to that conclusion.

C. It might seem that this choice supports the conclusion. If the ancestral species never lived anywhere other than Marlandia, then the present-day species could not have descended from this ancestral species elsewhere and only later, after the sea-level rise, migrated to Marlandia. That would help rule out an alternative explanation of how the present-day species survived the global sea-level rise. However, note that all we are told is that no fossils have been found anywhere other than Marlandia. Simply because no such fossils have yet been found does not indicate that these ancestral species never existed elsewhere. Fossils are often deeply buried and hard to find. After all, the fossils on Marlandia that are discussed in the argument were only recently found; perhaps other such fossils will soon be found elsewhere. Thus, this answer choice does not support the conclusion.

D. This does not provide any particular support for the argument. Note that it is not the present-day reptile species that is presumed to have survived on Marlandia when sea levels rose. Rather, it is the ancestral species that is presumed to have survived.

E. Correct. This rules out that the ancestral species could have survived the sea-level rise simply by living at sea. It also reduces the possibility that the ancestral species had also lived elsewhere than Marlandia and had only later—after the sea-level rise—migrated to Marlandia.

The correct answer is E.