Final answer:
The correct answer to complete the informal outline on what teenagers should know about hearing loss is 'Damage to eardrums cannot be repaired', as it aligns with the passage's focus on the permanent impact of loud noise exposure on hearing. The correct answer is option: d) Damage to eardrums cannot be repaired.
Step-by-step explanation:
When considering what teenagers should know about hearing loss, the given informal outline of the passage outlines that volume should be turned down while using earphones, and that genetics can also play a role. Based on the provided reference material focusing on environmental causes and irreversible damage due to loud noises, the statement that completes the informal outline is likely to be about permanent hearing damage due to noise exposure.
Damaged eardrums and the tiny hair cells in the cochlea, once destroyed, do not generally grow back, thus leading to permanent hearing loss. It's also stated that conductive losses in the middle ear can be partially overcome with hearing aids, and that cochlear implants can help where there's damage or loss of the cilia. However, damage specifically to the nerves in the cochlea is highlighted as being not repairable. Considering this, the completion of the outline is likely focused on the permanence of this damage.
Therefore, the answer is 'Damage to eardrums cannot be repaired' (d). Hearing loss is a serious issue and understanding that exposure to loud sounds, like rock music and construction equipment, can lead to sensorineural hearing loss, which is a permanent condition, is critical for teenagers to know in order to take proactive steps in protecting their hearing.