Nobody __________ absent today.

The correct answer is C: is. This question tests your knowledge of subject-verb agreement with indefinite pronouns. Indefinite pronouns like "nobody," "no one," "everyone," "someone," "anybody," "each," and "every" are always treated as singular, even though they might seem to refer to multiple people or things. Consequently, they always require a singular verb.

• "Are" and "were" are plural verbs and are incorrect because "nobody" is singular.
• "Have" is also a plural verb and does not fit the context of describing a state of being absent.

The rule is straightforward: if the subject is an indefinite pronoun ending in "-body," "-one," or "-thing," it takes a singular verb. Therefore, "Nobody is absent today" is the grammatically correct construction. This ensures that the verb properly agrees with the singular nature of the indefinite pronoun, maintaining grammatical accuracy in the sentence.