根据下面资料，回答题。
Studies over the past decade at the University of Utah show that hands-free cellphones are just as harmful to drivers as hand-held ones because it is the conversation, not the phone, that is distracting(分散) their attention. "Even though your eyes are looking right at something, when you are on the cellphone, you are not as likely to see it," says Professor David Strayer. "Ninety-nine percent of the time, it´ s not that critical (危急的 ), but that 1% could be the time a child runs into the street," he adds.
Dr. Strayer´ s studies have also found that talking on a cellphone is far more distracting than talking with a passenger. Listening to the radio, to music or to a book on tape also isn´ t as distracting, because it doesn´ t require the same level of interaction as a conversation. But even drivers may miss some details of a book on tape if their attention is focused on driving tasks. Some people can train themselves to pay extra attention to things that are important--like police officers learn to search faces in crowds.
And the Utah researchers have found a rare group of "super-taskers"--about 2.5% of the pop-ulation--who seem able to attend to more than one thing with ease.
Many more people think they can effectively do several things at the same time, but they are really turning their attention rapidly between two things and not getting the full effect of either.
Clearly, it is easier to put some tasks together than others. "Not all distractions are the same," says Dr. Strayer. Things like cleaning and working out can be done automatically( 自动地) while the mind is focused elsewhere. But doing homework and texting at the same time isn´t possible. Even talking and watching TV is difficult. "Just try talking with your wife while watching football. It´ s impossible," jokes Dr. Strayer.
What is the first paragraph mainly about?