Cell phones are very useful and they're great fun.But cell phones do have risks.If you have one，it is necessary to understand these risks，and learn __11__ enjoy your phone safely.__12__ can be a wonderful way to keep in touch with your friends.But bad people can also send messages.If you receive a rude or terrifying message，do not reply or forward (转发) it.__13__，
save the message and show it to your teachers or parents.If you receive a message saying that you __14__ a big prize，don't believe it. Sending pictures from a cell phone is fast， easy and fun.But make sure you send only pictures that you wouldn't mind other people __15__．And you are more likely to have an accident if you try to use your cell phone while __16__ the road.There are cars and buses to watch out for！Hang up your cell phone __17__ you walk. With your parents' help，you can keep your cell phone's __18__，you won't have to worry about receiving unwanted calls or messages！Remember not to talk on the cell phone too often or too long.Your parents will be __19__ if you spend too much money.__20__ your cell phone when you sleep.The sounds of rubbish messages may wake you up. (B)11.A.how B．how to C．what D．what to (C)12.A.Send messages B．Use cell phones C．Sending messages D．Us