A、To caution young people not to send texts while driving. B、To teach young people how to drive their cars safely. C、To persuade

"Where u at?" Those three words were the last text message Mariah West read before the violent car crash that took her life. It was the day before Mariah’s graduation from high school. She was on her way to a ball game and was getting directions. The eyewitness report says for no apparent reason, she lost control of her car, crossed the centre line, clipped a bridge, then flipped across two more lanes of traffic. No parent wants to receive that phone call. (26) So Dye, Mariah’s mother shares her story in a new documentary, "Texting Can Wait," which she hopes to send a clear message to teen drivers. This documentary shows that in just three seconds, if you’re going down the state road, you can cover the length of five football fields. A lot can happen in that amount of distance in that short amount of time. It’s not a matter of if you would have an accident, but when. The ten-minute documentary is available on the Internet and was produced by AT&T. One study has shown people who text while driving are six-to-eight times more likely to have an accident than drivers who are focused on the road. (27) According to the latest available government statistics, among the about 8 000 crashes on US highways in 2010, nearly 6 000 were due to distracted driving. The "Texting Can Wait" documentary is one of the tools AT&T is using in its campaign against distracted driving. (28)The ultimate goal of the campaign is to make sure teen drivers get the message that texting behind the wheel is an unacceptable and dangerous behavior—one that can wait until you’re out of traffic.
26. Why does Mariah’s mother share her story in a document?
27. What’s the main cause of crashes on US highways in 2010 according to the study of government?
28. What’s the ultimate goal of the campaign?