Me with physics sound waves and hearding (pic incl)

DB are units that might be good to add. 
They are louder as they use loud equipment or have practicals in which students talk.
It's more of a risk for teachers as they are exposed to it for every lesson they teach as students might only have one hour of it each day.
More likely reason is he's older so the level of pitch detection decreases with age.
f) the noise is reflected off the smooth surfaces and echoes

therefore, the efficiency is:

Ithink the answer is a