<p>Reviewing the attached brochure in advance of the seminar would be <u><b>exceptionally</b></u> helpful.</p>
<p>The correct answer is <b>(D) exceptionally</b>.</p>
<p>In this sentence, we are looking for an adverb that describes the level of helpfulness of reviewing the brochure in advance of the seminar. The adjective form of this word is "exceptional," which means "unusually good or outstanding." To form an adverb from an adjective, we typically add the suffix "-ly." Therefore, the correct adverb form is "exceptionally," which means "to an unusually high degree" or "extremely."</p>
<p>Here are the explanations for the other options:</p>
<p>(A) "Except" is a preposition that means "not including" or "other than." It does not fit in the context of the sentence.</p>
<p>(B) "Exception" is a noun that means "a case or instance that does not conform to a general rule." It does not work as an adverb in this sentence.</p>
<p>(C) "Exceptional" is an adjective that means "unusually good or outstanding." While it is related to the correct answer, it does not function as an adverb.</p>