Which sentence shows the main idea of the passage? We all know that driving while talking on a cell phone is dangerous. But did you know that driving while talking on a hands-free phone can be just as dangerous? Many studies have found that talking on a hands-free phone can increase the chances of an accident. Most people misunderstand the cause of cell phone driving accidents. They believe that using your hands to hold the phone while driving is the problem. It’s actually the brain that’s the problem. When you’re on the phone, your brain can’t focus as much on driving. Then you’re more likely to have an accident. A study by Carnegie Mellon University showed that just listening to someone else talk on a phone caused a 37 percent drop in concentration among drivers.