LEDs used in traffic lights are developed by Holonyak's students.

• A、 True
  
  

• B、False
  
  

• C、Not Given
  
  

When Holonyak invented LEDs, he believed that they would have a wide range of uses.

• A、True
  
  

• B、False
  
  

• C、Not Given
  
  

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Cell Phones:Hang Up or Keep Talking?

Millions of people are using cell phones today. In many places it is actually considered  41  (usual)not to use one. They find that the phones are more than a means of____42____(communicate)—having a mobile phone shows that they are cool and____43___(connect).

The____44____ (explode)around the world in mobile phone use make some health professional

worried.Some doctors are____45____(concern)that in the future many people may suffer health problems from the use of mobile phones. In England, there has been a serious debate about this issue. Mobile phone companies are worried about the negative ____46____ (public)of such ideas.They say that there is no____47____(prove)that mobile phones are bad for your health.

On the other hand, signs of change in the issues of the brain and head can be____48___(detect) with modern scanning equipment. What is it that makes mobile phones____49____(potential)harmful?  The answer is radiation.

As the discussion about their safety continues, it appears that it's best to use mobile phones less often. Use your regular phone if you want to talk for a long time.Use your mobile phone only when you really need it. Mobile phones can be very useful and convenient, especially in emergencies.In the future, mobile phones may have a____50____ (warn)label that says they are bad for your health.So for now, it's wise not to use your mobile phone too often.