Driving while talking on a hand-held mobile phone has long been considered a danger. But even drivers who use hands free devices are a nuisance – because they are slowing everyone else down, according to a study. David Strayer, a psychology professor in Utah University’s traffic lab, conducted a study involving 36 university students driving on motorways. Each used a hands free phone for half the trip but not for the other half. The students were told to obey posted speed limits and use turn signals but the rest of the driving decisions were up to them . What Strayer found is that when the drivers were distracted（使分心）by a phone conversation , they made fewer lane（车道） changes, drove slower and took longer to get where they were going. Fellow researcher Professor Peter Martin, who teaches civil and environmental engineering at Utat University, said,“Ordinarily a slower driver should be safer ， but that’s not the case when people are talking on a cell phone.” In general , drivers who used mobile phones while driving took three percent longer to drive along the same high-density route than drivers who didn’t. When stuck behind a dawdling(磨蹭的) driver , it took them between 25 and 50 seconds longer to switch to an open lane to overtake. Those delays can add up when you consider studies that suggest as many as 10 percent of US drivers are using a cell phone at any one time. And delays in traffic streams of very small amounts can grow into massively when drivers are crossing a  highway.” Our next step is to use computer models to determine just how much those delays are costing drivers in time and in extra fuel costs,” Martrin said. 63. What does the underlined word in the first paragraph mean? A. A person who is a volunteer.         B. A person who breaks the traffic law C. A person who is annoyed by others.   D. A person who causes trouble 64. Which of the following is TRUE , according to Martin? A. The more slowly a person drove, the safer he was. B. Measures should be taken to stop using mobile phones. C. Drivers using hand-held phones had less effect on traffic than those using hands free phones D. Driving while using mobile phones could cost drivers time and money. 65. The passage is mainly about . A. traffic conditions in rush hours B. the use of mobile phones in the USA C. using hands free devices behind the wheel D. a comparison between hand-held phones and hands free ones