Some of the most popular attractions across America are the many free concerts offered to public throughout the year. These involve not only amateur performers, but professional artists as well. The public parks of many cities across the country usually have bandstands and large lawns. As a service to citizens, they rent out space to performers free of charge. Amateur groups, with nothing more than a desire to perform. offer their talents freely to public. Semi-professional artists are pleased to get the chance to perform. before the public to perfect their craft and nurture the hope of being discovered before beginning a professional career. Famous professionals also give free concerts to make contact with their admiring fans. Often such concerts are sponsored by a large corporate organization and offered to the public free of charge as a cultural service and support for the arts. The free concerts feature all kinds of music from rock and roll, jazz, country, western to the classics. In addition, free performances may include the plays of Shakespeare or experimental theatre of modern dramatists. In New York's Central Park there has long been a summer Shakespeare festival which draws huge crowds to the free performances. Of these concerts the ones held on a summer evening in the park are the most popular. They take on a festive air. Friends and groups gather together after work and spread out a blanket on the lawn facing the performers' stage. The early comers get the best locations and enjoy a picnic supper while it is still daylight. The free seating is on a first come basis. Therefore, by the time the concert begins, as many as five thousand or more people may be in attendance. The concerts usually begin at 8 p. m and are performed under the stars. The sound is made sufficiently loud so that no matter where one chooses to sit, he can hear very well. The only disturbance may be the sound of an overhead airplane on its final approach to an airport or the far-off siren(警笛声) of an ambulance on its way to the hospital. This matters little! What counts is to soak up the atmosphere created by the music and to be with friends in the fresh open air. The best part of it all is that it's free! Many American parks give free concerts on their lawns because they______.