Footracing is a popular activity in the United States.It is not only seen as a competitive sport,but also as a way to exercise,and to donate money _ .Though serious runners may spend months training to compete,other runners and walkers might not train at a11.Those not competing to win might run in an effort to beat their own time,or simply to enjoy the fun and exercise.People of all ages, from those less than one year old to those in their 80s, enter into this sport.The races are held on city streets,on college campuses,through parks,and in suburban areas,and commonly 5 to 1 0 kilometers in length. The largest footrace in the world is the 1 2-kilometer Bay to Breakers race that is held in San Francisco every spring.This race begins on the east side of the city near San Francisco Bay and ends on the west side at the Pacific Ocean.In 1 993 there were 80,000 people running in this race through the streets and hills of San Francisco.In the front are the serious runners who compete to win,and who might finish in as little as 34 minutes.Behind them are the thousands who take several hours to finish.In the back of the race are those who wear costumes just for fun.In 1 993 there was a group of men all of whom dressed up like Elvis Priestly.There was a group of firefighters who were all tied in a long line and were carrying a fire--hose .One year there was a wedding party in which the bride dressed in a long white gown and the groom wore a tuxedo .They threw flowers to by-standers,and were actually married at some point along the route. The main purpose of this text is to  _  .
describe a popular activity encourage people to exercise make fun of runners in costume give reasons for the popularity of footraces