You see the lightning           it happens, but you hear the thunder later.

A．the instant       B．for an instant          C．on the instant        D．at instant

You see the lightning         it happens, but you hear the thunder later.

A．the instant                  B．for an instant       C．on the instant       D．at instant

31.   You see the lightning _____ it happens, but you hear the thunder later.

 You see the lightning _____ it happens, but you hear the thunder later．

       A． the moment   B． for the moment   C． at the moment  D． in a moment

  This is what happens when there is a thunderstorm. First you see a sudden flash(闪亮) of bright light. A few seconds later you hear a loud rumbling sound. This quick flash is called lightning, and the loud sound is called thunder. Lightning is colorful, but it can cause serious problems.

  Lightning is electricity that is moving very rapidly. It may be moving between a cloud and the ground, between two clouds, or between two parts of the same cloud. The lightning heats the air around it. This hot air expands(扩大)，or gets bigger, and it causes the air to move in waves which pass you in a series(系列), one after another. For this reason, you may hear many rumbles and not just one sound.

1．A good title for this selection is　　   .

A. Air Waves

B. Lightning and People

C. The Weather is Not Beautiful All of the Time

D. Thunderstorms

2．The word “rumble” in this passage means　　   .

A. a sharp voice

B. a loud and joyful sound

C. a sudden flash

D. a deep, heavy continuous sound

3．When you hear thunder, you may hear a series of loud sounds and not one big sound. This is because　　    .

A. the hot air moves between two clouds

B. the air waves pass one after another

C. the thunder comes after the lightning

D. the lightning comes after the thunder

4．Which of these is NOT TRUE about thunder and lightning?

A. Lightning may move between a cloud and the ground.

B. Thunder is a very bright light in a thunderstorm

C. Lightning is electricity.

D. Lightning heats the air around it and causes the air to move in waves.

5．Lightning always moves　　    .

A. between two clouds　　　　　　　　  　　　　　　　　B. in waves

C. in a series　　　　　　　　　　　　　　　　　　　　  D. rapidly