Increases in the length of a person's muscles have been shown to

D IMO

Combining both statements we can infer this.

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I've marked C but in hindsight - it is a more extreme option while D is grounded - making it a better option

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it is given in the passage that stretching and drinking at least 64 ounces of water increases muscle and it will improve physical activity in the case of some individual. Hence D[ A program of stretching and drinking at least 64 ounces of water will improve the performance of some individuals during physical activity].

Official Explanation

The question asks for something that "can be correctly inferred," making this an Inference question.

According to the stimulus, some people can lengthen their muscles by stretching and drinking a certain amount of water each day, and lengthened muscles improve physical performance and reduce the risk of injury from physical activity.

It's often hard to predict an answer to Inference questions, but think about what you're given here. There's a plan to lengthen muscles and a benefit to be had from it; the right answer will likely point out that if some people follow the plan, they'll get the benefit.

Correct choice (D) states that engaging in stretching and water drinking can improve the physical performance of some people. The word "some" is key--it can't be concluded that all people can benefit from stretching and drinking enough water, because only some people can lengthen their muscles from this sort of a regimen.

(A) and (C) are extreme. There's not enough information to say that those who stretch and drink water do not run any risk of injury--just that some people who do so will lower their risk. Nor is there enough information to say that stretching and drinking water is the best way to increase performance and reduce the risk of injury--just that it is one way of doing so.

(B) also does not follow from the statements given. Just because the risk is lowered for some who stretch and drink 64 ounces of water daily, it does not have to be true that those who do not engage in such activity have a high likelihood of injury.

(E) is also unsupported. A program of both stretching and drinking 64 ounces of water can lengthen muscles; either alone may not be effective.
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