Explanation:

The sentence states that the athletes' performance in the competition silenced his critics. This implies that the athletes performed exceptionally well, as their performance was able to quiet the individuals who doubted or criticized them. Therefore, the two answer choices that fit the meaning of the sentence and produce completed sentences that are alike in meaning are "stellar" (meaning excellent or outstanding) and "exceptional" (meaning extraordinary or remarkable).

Reasoning:

- "Stellar" means excellent or outstanding. If we use this word to complete the sentence, it would read: "The athletes' stellar performance in the competition silenced his critics." This sentence conveys the idea that the athletes' performance was exceptional and silenced those who criticized them. It aligns with the meaning of the original sentence.

- "Exceptional" means extraordinary or remarkable. If we use this word to complete the sentence, it would read: "The athletes' exceptional performance in the competition silenced his critics." This sentence also communicates the idea that the athletes' performance was outstanding and silenced their critics. It has a similar meaning to the original sentence.

Incorrect Options:

- "Mediocre" means of average or ordinary quality. If we use this word to complete the sentence, it would read: "The athletes' mediocre performance in the competition silenced his critics." This sentence contradicts the meaning of the original sentence, as it suggests that the athletes' performance was average or ordinary, which would not silence their critics.

- "Lackluster" means lacking in vitality, enthusiasm, or effort. If we use this word to complete the sentence, it would read: "The athletes' lackluster performance in the competition silenced his critics." This sentence also contradicts the meaning of the original sentence, as it implies that the athletes' performance was unimpressive or uninspired, which would not silence their critics.

- "Middling" means of average or moderate quality. If we use this word to complete the sentence, it would read: "The athletes' middling performance in the competition silenced his critics." This sentence contradicts the meaning of the original sentence, as it suggests that the athletes' performance was average or moderate, which would not silence their critics.