Conclusion: 'SuperOXY' water would be useless in improving physical performance.

The bold portion "the only way to get oxygen into the bloodstream so that it can be absorbed bye the muscles is through the lungs" is a premise supporting the conclusion.

So I have to find the option that, if incorporated in the argument, will also function as a premise i.e. it will also support the conclusion. So in short, I am trying to find the option that strengthens the conclusion.

Option (A) is incorrect because it says that water lost can be replaced by tap water. It doesn't say how or why SuperOXY is useless in improving physical performance.
Option (B) says that amount of oxygen is already more than what the muscles can absorb. This means drinking SuperOXY will not improve physical performance because muscles anyway cannot absorb the extra oxygen. This option strengthens the conclusion. Hence this is the answer.
Option (C) says that people turn in great performance without this water. But it doesn't say that this water cannot further improve their performance.
Option (D) says that frequent physical exercise increases the body’s ability to take in and use oxygen. It doesn't say anything about how this water does not improve performance.
Option (E) says there are other factors affecting human physical performance but doesn't say that SuperOXY doesn't affect human physical performance.
Answer (B)