Read the Original Sentence Carefully, Looking for Errors:
The underlined portion of the sentence begins with the relative pronoun "that," referring to "athletes." The GMAT requires that the relative pronoun “who” be used when referring to people. "That" may only be used as a relative pronoun when referring to things or animals. For example, it would be correct to say “the artist who created the sculpture” but not "the artist that created the sculpture."
Scan and Group the Answer Choices:
A quick scan of the choices reveals a 3-2 split based on the pronoun at the beginning. (A) and (B) both begin with “that,” while (C), (D), and (E) begin with “who.”
Eliminate Wrong Answer Choices:
Immediately discard (A) and (B), because they use the pronoun “that” to refer to a person.
In (D) and (E), "at one time" is wordier than the other choices' "once." Also, these answers move the phrase "due to catastrophic injury" to the earlier part of the underlined portion, This causes the long sentence to read less smoothly. The GMAT prefers clear, concise language. Since the point of the sentence is that many athletes who lost their ability to participate can now get it back, everything else, such as why they lost their ability, should be placed to minimize the disruption of flow. So, for example, “athletes who have lost their ability due to injury” is preferable to “athletes who, due to injury, have lost their ability.”
(C) uses the correct pronoun, "who," and avoids the problems in (D) and (E) created. Again, the GMAT prefers concise writing. (C) is the correct answer.
TAKEAWAY: Once the errors from the original sentence have been taken care of, consider stylistic choices. The GMAT prefers clear, concise, direct language whenever possible.