Neither the principal nor the teachers ___________ able to give a satisfactory explanation.

The correct answer to fill in the blank in the sentence is "were."

Explanation:

In this sentence, "neither... nor..." is a correlative conjunction that connects two subjects. When using "neither... nor...", the verb should agree with the nearest subject, which in this case is "teachers," a plural noun. Therefore, the verb should also be in the plural form. "Were" is the plural past tense form of the verb "to be," making it the correct choice for this sentence.

The completed sentence reads: "Neither the principal nor the teachers were able to give a satisfactory explanation."

This structure emphasizes that both the principal and the teachers failed to provide a satisfactory explanation, indicating a lack of clarity or understanding on their part regarding the situation in question.