A résumé is a history of past work experience,
and when it is well written it is also a savvy piece of marketing, but there is one thing it is definitely not; a chronology of past performance.(A) and when it is well written itis also a savvy piece of marketing, but there is one thing it is definitely not; a chronology of past performance.
(B) and when it is well written it is also a savvy piece of marketing, but there is one thing it definitely is not. It is not a chronology of performance in the past.
(C) and when it is well written itis also a savvy piece of marketing, but there is one thing a resume definitely is not: a chronology of past performance.
(D) and when it is well written itis also a savvy piece of marketing, but there is one thing It definitely is not. It is not a chronology of past performance.
(E) and when it is well written itis also a savvy piece of marketing, but there is one thing it is definitely not. It is not a chronology of past performance.
The best answer is (d). Choices (a) and (e) are incorrect because the verb phrase "is not" is separated by the word "definitely." Choice (c) makes use of inappropriate punctuation and choice (b)'s "of performance in the past" is wordy and awkward compared to choice (d).