Hi anksm22,

This is a rarer CR prompt - we're asked to replace the bolded statement with one of the 5 options so that the effect is the same. We'll need to understand the author's logic and understand the role of the bolded statement.

The Facts:
-One factor that limits human physical performance is the amount of oxygen that is absorbed by muscles from the bloodstream.
-Gyms and Health Clubs sell "SuperOXY" - a water that has extra oxygen dissolved in it.
-The amount of oxygen in the blood of someone who is exercising is already MORE than the muscles can absorb.

The Conclusion:
-This type of oxygen-infused water would be USELESS in improving physical performance.

The Logic:
The first sentence tells us that the amount of oxygen in the bloodstream will affect one's physical performance, so the idea that "more oxygen" will improve physical performance seems logical. Gyms/Clubs are selling water with "extra oxygen" in it, but we're told that this type of water would be USELESS ...SINCE.... The word "since" introduces the reason WHY this oxygen-infused water would be useless, so we need an answer that would provide a reason WHY the oxygen-infused water would be useless.

The given reason WHY the water would be useless is that the bloodstream already has MORE oxygen than the muscles can absorb, so there's NO WAY for extra air in the BLOODSTREAM to improve one's physical performance. Remember from the first sentence that the subject is to increase physical performance with extra oxygen, so we need an answer that stays on topic and is similar to the given reason for why that water is useless.

The only answer that fits is C - it stays on topic and tells us how the oxygen ACTUALLY would have to get into the bloodstream (by something other than the water).

GMAT assassins aren't born, they're made,
Rich