阅读理解。

      In many high schools, there are strict rules about using mobile phones. If your phone rings in class,

for example, the teacher will be very angry.

     Every mobile phone has a ringtone (铃声). It tells you that someone is calling you. Now,there is a ringtone

called "mosquitotone (蚊子铃声)". Using it, students can receive calls and text messages (短信) in class but

the teacher will not realize what is happening. How?

     Mosquitotone has a special sound. Only children and teenagers can hear it. As we get older,we are unable

to hear some sounds with high frequencies (频率). As a result,a child or teenager can hear the mosquitotone

ringtone, but it's inaudible to someone 20 or older.

     But sometimes,people over 20 can hear the ringtone. One British student's phone uses mosquitotone.

In class, the student's phone rang. The 32-year-old teacher looked at the student and became unhappy. "I

heard that. You know the rule:no mobile phone in class."

     Not all the students are interested in mosquitotone. Jerry Jones,a high school student of 17, says, "Using

mosquitotone too often is bad for our hearing. I may use it for pleasure,but not in class. It's unfair to the

teachers!"

     What do parents think of mosquitotone? "I think it is perfect for places like movie theaters," says Connie

Neeson, 44. "Think about it. Yon're watching a film and someone's mobile phone rings. Mosquitotone is good

because many people don't hear it. However,it also has a bad influence on their study if students use it in

class."

1. Mosquitotone works because ________.

A. it is very loud

B. it has no sound

C. it has a beautiful sound

D. it uses high frequencies

2. The under lined part "it's inaudible to" means "________".

A. it can't be seen by

B. it can't be heard by

C. it isn't popular with

D. it isn't healthy for

3. The 32-year-old teacher felt unhappy because the student ________.

A. was late for class

B. didn't do his homework

C. couldn't answer her question

D. was using a mobile phone in class

4. Connie Neeson thinks that mosquitotone ________.

A. has no bad influence

B. is unfair to the teachers

C. has its advantage and disadvantage

D. can't be used in any public place