单项选择题

A recent study, published in last week’s Journal of the American Medical Association, offers a picture of how risky(冒险的) it is to get a lift from a teenage driver. Indeed, a 16-year-old driver with three or more passengers is three times as likely to have a deadly accident as a teenager driving alone, while the risk of death for drivers between 30 and 59 decreases with each additional passenger.
The authors also found that the death rates for teenage drivers increased sharply after 10 p.m., and especially after midnight. With passengers in the car, the driver was even more likely to die in a late-night accident.
Robert Foss, a scientist at the University of North Carolina Highway Safety Research Center, says the higher death rates for teenage drivers have less to do with “really stupid behavior” than with just a lack of driving experience. “The basic issue,” he says, “is that adults who are responsible for issuing licenses fail to recognize how complex and skilled a task driving is.”
Both he and the author of the study believe that the way to mitigate (使……缓解)the problem is to have states set up so-called graduated licensing systems, in which getting a license is a multistage process. A graduated license requires that a teenager first prove himself capable of driving in the presence of an adult, followed by a period of driving with night or passenger limits, before graduating to full driving licenses.
Graduated licensing systems have reduced teenage driver crashes, according to recent studies. About half of the states now have some sort of graduated licensing system in place, but only 10 of those states have limits on passengers. California is the strictest, with a new driver under 20 forbidden to carry any passenger (without the presence of an adult over 25) for the first six months.

The present situation in about half of the states is that the graduated licensing system （）

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