Answer: c. The elementary school Munhall has many bright, young teachers.
An essential appositive is a phrase or short description placed before a noun or pronoun, as an explanation. It is an important part of a sentence since the sentence will have a different meaning than it originally would, and so it does not need to carry a comma.
Options A, B, and D all have elements that can be done away with and carry commas in the indicative positions, so they are wrong.