The correct answer is "drift."

"Waft" is a verb (or noun) that means to pass (or cause to pass) easily/gently through the air or as if through the air. 

This makes "drift" (carried slowly by a current of air or water) making it the correct synonym.

"Coach" can be a noun meaning an athletic instructor, or a verb meaning to instruct one in a sport. A "coach" can also be a noun meaning "carriage," (generally horse-draw) which is the correct answer.

"Revival" means Recovery; Death means the end of one's life; Monument is usually a figure or symbol that represents something or someone; Province is a territory usually part of a larger state or country; and Possibility is a potential outcome.

"Unrest" means turmoil. "Peace" and "calmness" are antonyms of "unrest" and mean tranquiity. "Enjoyment" means pleasure or amusement. "Democracy" is a representative government.

A "preamble" is an introduction that appears before the main body of work, so "introduction" is the correct answer. For clarification, "finale" and "conclusion" each mean an ending, a "tome" is a long and ponderous book, and an "index" is a list of subjects that appear at the end of a book and the numbers of pages on which one can read about them in that book.

"Retrospect" means recollection, remembering past events, hindsight. You might be able to infer this meaning from the word's roots; "retro-" means backwards, as in the word "retroactive" (applying to a span of time in the past) and "spect" means look or see, as in the word "spectacles" (glasses). So, "hindsight" is the correct answer. For clarification, "optimism" is a positive feeling about future events, "prosperous" means wealthy or successful, "exuberant" means lively, and "evanescent" means fleeting.

"Prescience" means foresight or the ability to know about something before it has actually happened. "Shortsightedness" and "myopia" are synonyms, so we can eliminate those. "Improvidence" means poor planning for the future, and "unpredictability" the quality of not being able to be foreseen. "Foreknowledge," which means foresight or knowledge of something before it happens, is the only choice that works.

"Impartial" information is unbiased and uncorrupted by personal intervention. For clarification, someone who is "bashful" is easily embarrassed; "harangue" means berate or criticize.

"Unaware" means unknowing. "Informed" means knowing, so it cannot be the correct answer, because it is an antonym, not a synonym, of "unaware." None of the other answers are close in meaning to "unaware": "obvious" means overt or palpable; "complete" means lacking nothing necessary; and "precise" means exact. 

"Uncertain" means not known with certainty, so "unknown," an adjective that means not known, is the correct answer. "Conclusive" is an antonym of "uncertain"; it means definite or indisputable. None of the answer choices have a meaning related to that of "uncertain": "bright" means shining or emiting lots of light; "idiotic" means stupid or foolish; and "frequent" means occuring often or repeated.