<p style="">The correct answer is (C) Were.</p><p style="">This sentence is an example of the "inverted conditional," specifically the "inverted second conditional," which is used for unreal or hypothetical situations in the present or future. The standard form of the second conditional is "If + subject + simple past verb, subject + would + verb." When using the inverted form for emphasis or a more formal tone, "if" is omitted, and the sentence starts with the past tense form of the verb "to be," which is "were," followed by the subject.</p><p style="">Let's break down the sentence:</p><ol style=""><li>"______ it not for Alex's help," is the if-clause in the conditional sentence. It implies a hypothetical situation where Alex didn't help.</li><li>"the annual conference would not be such a huge success," is the result clause, indicating what would happen (or wouldn't happen, in this case) if the condition in the if-clause weren't met.</li></ol><p style="">(C) "Were" correctly completes the sentence: "Were it not for Alex's help, the annual conference would not be such a huge success." This construction, "were [subject] not," is a formal, somewhat archaic way of saying "if [subject] were not," and it's used for hypothetical or contrary-to-fact situations, which fits the context of the sentence.</p>