Loud music is most dangerous to hearing when it is played through stereo headphones. Teenagers who now listen to music at dangerously loud levels choose to do so despite their awareness of the risks involved. No other cause of hearing loss in teenagers is as damaging as their listening to loud music through stereo headphones. A few headphone manufacturers already plan to market stereo headphones that automatically turn off when a dangerous level of loudness is reached.
Increases in the occurrence of hearing loss among teenagers are due in part to their listening to loud music through stereo headphones. So a group of concerned parents is recommending that headphone manufacturers include in their product lines stereo headphones that automatically turn off when a dangerous level of loudness is reached. It is clear that adoption of this recommendation would not significantly reduce the occurrence of hearing loss in teenagers, however, since almost all stereo headphones that teenagers use are bought by the teenagers themselves.
Which one of the following, if true, provides the most support for the argument?