单项选择题

A range of new commuting bikes are promising to make everyday travel by bicycle as comfortable and fashionable as it is cheap. They also allow you to combine workout with transportation. "It"s convenient; it keeps me fit; and it saves money," says Scott Infanger, a professor at the University of North Alabama, who regularly bikes his daughter----Elizabeth, 7, to school on the way to his nearby office.
Bike stores and manufactures across the nation are reporting a significant rise lately in sales. "They"re selling out of all the commuting bikes ---all bikes, actually ----that they can get their hands on," says Bill Fields, a consultant who has followed the bicycle industry for decades. Fields predicts a 20 percent increase in the "comfort bikes", which includes for decades,by the end of year.
One big block to a rise in bike commuting is a concern about safety. In 2006,773 people were killed bicycling, and tens of thousands injured. Rutgers researchers who compared the safety of walking ,biking, and diving found that, per kilometer traveled, bicycle fatalities(死亡人数）were 11 times higher than car fatalities.
Still, experts say, the story has anther side. In the Rutgers study, the rate of pedestrian(行人)fatalities. One Danish study published in the Archives of Internal Medicine found that because of the health benefits of bicycle commuting, the death rate among noncyclists was 39 percent higher than among the bikers. According to Professor Infanger, bike commuting is ______.