在海面上有一只舰船，上面有一台超声测位仪，为了测出海底有多深，竖直向海底发射超声波，经过4s接收到反射波，超声波在海水中传播速度约1500m/s，问该处海底有多深？若用上述方法向月球发射超声波，能否测出地球到月球的距离？

It's easy to take your hearing for granted until it's too late.

With the wide    1   _(popular) of digital entertainment products, it is not uncommon to see people wearing headphones and listening to music    2    running in the park or using public transport. And the volume is often so loud that people around    3    can hear the music as well.

However, doctors warn that such behavior can    4   _(potential) damage their hearing. "In noisy places, people tend   5  _(turn) the volume up to get the same clarity of sound. Unfortunately, that can damage the hearing   6  people being aware of it," said Feng Yongfeng, chief ENT physician at Beijing Tian'an Hospital.

After Spring Festival, the hospital witnessed   7   slight increase in the number of teenagers coming in with hearing problems,  8   Feng attributed to them wearing headphones at home for long periods during the holiday. Feng said both in-ear and overhead headphones can harm the ears and    9   (advise) against using them for long periods. He said if you do use headphones it is worth    10   (invest) in the highest quality you can afford.