First it was jogging. Then aerobics . Not too long ago, Americans discovered race walking.        Now Americans are into a newfitnesscraze. They'retaking up bicycling. Over hills and down mountainsides and across quiet country roads, Americans are busily rolling along.        The number of adults who ride for fitness is around 17 million, an increase of 70 percent over four years ago. Twice as many women as men are coming to the sport. Americans arefalling in love withbiking because it has speed, the benefitsofjoggingand beautiful scenery.        Bicycling is a very appropriate sport, which is important to people who injured their knees while jogging or whosejointsareachingfrom aerobics. And biking is a real awakening for people who have been into race walking in the past. Race walking isas dull as watching paint dry.        The most popular kind of bicycle for people who are new to the sport is the mountain bike, which has afixed framewith wide tires andupright handles. Mountain bikes also have manygears  to make it easier to climb hills. About 5 million Americans ride mountain bikes, compared with 200,000 who rode them only five years ago.        Costsrangefrom about $130 for abottom-of-the-linebicycle to more than $2,700 for an expensive bicycle.        Mountain biking has attracted somepeoplewho race down the sides of mountainslike a bat out of hell. But most riders ride slowly and theyrarelyventurefar from home.        The biking craze has brought an unexpected profit  to clothing and bicycle accessory  makers. Last year, bikers paid $ 630 million for biking clothes and accessories.        Bicycling seems likely to continue its fantastic growth. The main idea of the article is   _
riding a bicycle is one of the most dangerous sports in prefix = st1 /America. Americans are rolling along. bicycling is the latest fitness craze to hit America. most people in Americawant to own a hand-made bicycle that can cost more than $ 2,700.