A Middle-Aged Psychology Professor Has Been Tipped Off by One

A middle-aged psychology professor has been tipped off by one of his students that cell phones are going off in the classroom.The professor does not recall hearing a cell phone go off anytime in the last few days in class.What is the most likely explanation?

A) The students that told the professor about the cell phones is playing a joke on his teacher.
B) The students have downloaded a high-pitched ring tone that the professor cannot hear because of a loss of hair cells.
C) The students have downloaded a low-pitched ring tone that the professor cannot hear because of a loss of hair cells.
D) The professor has a severe conductive hearing loss.