Choose the option that grammatically completes the given sentence:

Neither the choir director nor the singers _______________ prepared for the unexpected blackout during the performance.

The correct answer is were.

Step-by-Step Explanation:

1. Understand Subject-Verb Agreement with Correlative Conjunctions:
When two subjects are connected using correlative conjunctions such as "neither... nor" or "either... or", the verb must agree in number (singular or plural) with the subject closest to it. This rule is often referred to as the rule of proximity.

2. Identify the Subjects in the Sentence:
- First subject: the choir director (singular)
- Second subject: the singers (plural)

3. Apply the Rule of Proximity:
The blank follows the second subject, "the singers", which is plural. Therefore, we need a plural verb in the past tense to complete the sentence correctly.

4. Evaluate the Options:
- were: Plural past tense verb. Matches the plural subject "singers".
- was: Singular past tense verb. Incorrect because "singers" is plural.
- has been: Singular present perfect verb. Incorrect subject agreement.
- is: Singular present tense verb. Incorrect subject agreement and tense.

Thus, the grammatically correct sentence is: "Neither the choir director nor the singers were prepared for the unexpected blackout during the performance."