lheiannie07 wrote:Whorfian tubules have an inside diameter equal to their length, a density half that of water, and a mass that is immeasurably small. A physicist isolated an entity less dense than water, with insufficient mass to measure, and a length exactly equal to the diameter of its inside.

It would be certain that the physicist had isolated a Whorfian tubule if it were concluded by the physicist that

A. the physicist had been looking specifically for Whorfian tubules
B. Whorfian tubules are the only entities of immeasurably small mass with an inside diameter equal to their length
C. the density of what he had isolated was exactly half that of water
D. Whorfian tubules are only found under the conditions that the physicist had duplicated
E. Whorfian tubules were the only entities half the density of water with an immeasurably small mass

Can some experts explain the best option?

OA B

This question doesn't feel terribly representative of GMAT, CR questions, but here's the gist.

A physicist isolated an entity with the following characteristics
- it is less dense than water
- is has insufficient mass to measure
- it has a length equal to its diameter

We're told that Whorfian tubules have those characteristics. But it's surely possible that other entities have those characteristics, right? Thus, in order to know for sure that the entity in question is a Whorfian tubule, it would be helpful if we knew that only Whorfian tubules possessed some of the aforementioned traits.

This is what B gives us. If only Whorfian tubules have mass too small to measure and a length equal to its diameter, and we just found something with mass too small measure and a length equal to its diameter, well, it stands to reason that we've found a Whorfian tubule.