短文填空
The world is filled of many interesting s  . Some are unpleasant to our ears w       others are very pleasant to hear. In single day you probably hear hundreds of sounds. All sounds are d. Some may be loud, some sounds are high, others are low, some sounds are useful.
W      sound 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 d   .Some sounds are harmful. When planes fly low over the land, the very loud sounds can damage ( 毁坏 ) the house. Very l   sound can even make people deaf.
We know sound travels about one kilometer in three seconds. In a thunder storm you see the lighting f    and then hear the thunder. This is because light travels much f      than sound. Next time you see lighting count the number of seconds before you h   the thunder. Divide this number by 3. This will tell you how m  kilometers away the thunder storm is.