Answer: A. could not be heard above the voices in the hallway.
Explanation: A predicate is the part of a sentence or a clause that contains the verb and that states something about the subject. The main characteristic of a predicate is that it must have a verb (a predicate could be just the verb of a sentence), so from the given fragments, the one that represents a complete predicate is the corresponding to option A, because it is the only one that contains a verb "could be heard".
