Answer:
Jack is an incredible linguist who is proficient in seven (different) languages.
Explanation:
Redundancy in the needless repetition of words, phrases, sentences, paragraphs, or ideas. By repeating words with the same or similar meaning we gain nothing. For example, in the given sentence, there is no need to say that Jack has the capability AND proficiency. It's enough to say one or the other, that he is capable of conversing in OR that he is proficient in seven different languages. We could even go as far as discarding the word <em>different</em>, as it's understood that Jack speaks seven different languages since there are no seven same languages, but it isn't as necessary as it is with other words.
Its C because adverbs usually end with -ly
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