Answer:
Either A or B
Explanation:
It really depends what kind of speech but your best bet is A if its a politician making a speech and B if it's a teacher/professor.
The fragment that is made up of a complete predicate is option A. "could not be heard above the voices in the hallway"
In grammar, the predicate is defined as the part of the sentence that contains the verb and gives information about the subject.
Option A is the only option that contains a verb, in this case "could" and it is providing information about a subject we don´t know. The only options lack verbs,
