Neither Ali nor Ahmed __________ completed the task.

The correct answer is "has". This question tests your knowledge of subject-verb agreement when using correlative conjunctions like "neither... nor." The rule for "neither... nor" can be a bit tricky, but it's straightforward once you understand it.

• Rule of Proximity: When two or more subjects are joined by "neither... nor" or "either... or," the verb agrees with the subject that is closest to it.
• Applying the rule: In the sentence "Neither Ali nor Ahmed __________ completed the task," the two subjects are "Ali" and "Ahmed." Both "Ali" and "Ahmed" are singular nouns. The subject closest to the blank (and thus the verb) is "Ahmed."
• Singular verb: Since "Ahmed" is singular, the verb must also be singular. "Has" is the singular form of the verb "to have" in the present perfect tense, which is appropriate here. "Have" is plural.

Therefore, the correct sentence is: "Neither Ali nor Ahmed has completed the task." This ensures proper subject-verb agreement, making the sentence grammatically sound.