Think about the last time you dropped a stone into water. Do you remember how the waves started? They began where the stone met the water and then moved outward.

Just as waves in water take time to move,so sound takes time to move in air. Sound takes time to travel.

  Perhaps you have noticed the time that passes between a flash of lightning and the thunder. You may have heard the sound of a baseball bat hitting a ball an instant after you saw it happen.

  Both light and sound take time to travel. However,there is a great deal of difference in their speed. In one second,sound can travel about1,000 feet through air. During this same time,light can travel more than186,000 miles！

  When something makes a sound some distance away,you can often see the action before you hear the sound. As sound travels,vibrations are passed on from one molecule to another. The farther the sound has to travel,the longer it takes.

(   ) 1. Which of these is WRONG?

   A. " Sound and wave" means"水花和水波".

   B. "Lightning and thunder" means"閃電和雷聲".

   C. "Instant and second" means"瞬息和秒鐘”.

   D. " Action and vibration" means"動作和振動".

(   ) 2. Sound takes time to move in air just as         .

   A. waves   B. trains   C. buses   D. cars

(   ) 3. When we drop a stone into water,we can see         .

   A. nothing

   B. the waves start where the stone meets the water and then move outward

   C. the waves start far from the stone

   D. both A and C

(   ) 4. Which of these is RIGHT?

   A. You may hear the sound of a baseball bat hitting a ball,then see the action.

   B. You may hear the thunder before you see a flash of lightning.

   C. Light takes no time to travel.

   D. The farther the light has to travel,the longer it takes.

(   ) 5. Which of these is NOT right?

   A. In one second,sound can travel about340 meters through air.

   B. In one second,light can travel about300,000,000 meters.

   C. One foot is longer than one meter.

   D. One meter is shorter than one mile.

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