Please answer the following question: Write a multi-choice question for the following article, with the given choices and answer: Article: Mobile phones help us easily find people anywhere at any time. A mobile phone can include many things, such as games, music and Internet surfing. Today, 4,600,000,000 people around the world have mobile phones, according to CBS News. However, using mobile phones too often may cause cancer . It's reported that people who used a mobile phone for 10 years or more were more likely to get cancer. The advice below may help you reduce the risk of cancer: An earphone gives out much less radiation than phones. However, you should take it off your ear when you're not talking to anyone. Your phone gives out radiation when you talk or text , but not when you're listening or getting messages. Listening more and talking less can lower the risk of cancer. Hold the phone away from your body when you're talking, not against your ear. Also, don't keep it in your pocket. Phones gives out less radiation to send texts than to carry a person's voice. Texting also keeps radiation away from your head. Do not use your mobile phone when the signal is weak. Fewer signal bars on your phone mean that the phone needs to give out more radiation to work. Make and take calls when your phone has a strong signal. Options: A the development and advantages of mobile phones B the reason why mobile phone radiation causes cancer C how to protect ourselves from mobile phone radiation D the best ways to use mobile phones to communicate Answer: C how to protect ourselves from mobile phone radiation Question:
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The passage mainly talks about _ .