The world   (1)   many interesting sounds. Some are unpleasant to our ears while   (2)   are very pleasant to hear. In a single day you probably hear   (3)   sounds. All sounds are different. Some   (4)   loud, some sounds are high, others are low, some sounds are useful.

  (5)   sounds we can’t talk or listen to each other. The ringing of the alarm clock wakes people up. The hooting(鸣笛声) of a car warns people of danger.

Some sounds are harmful. When planes fly low   (6)   the land, the very loud sounds can damage(毁坏) the houses. Very loud sounds can even make people deaf.

We know sound travels about one kilometer in three   (7)   In a thunder storm(雷雨) you see the lighting(闪电) first and then hear the thunder. This is because light travels   (8)   than sound.

Next time you see lighting, count the number of seconds before you hear the thunder. Divide(除以) this number   (9)    This will tell you   (10)   kilometers away the thunder storm is.