From a primitive form of locomotion to a sophisticated pastime and competitive sport, swimming has evolved. Swimming is a demanding sport that works almost every muscle group and calls for extensive training. In competitions, swimmers usually compete for the fastest time using a particular swimming stroke to cover a given distance. In addition, swimmers strive to develop their long-distance swimming endurance. Swimming has become such a complex competitive sport—one incorrect stroke can cause a competitor to be disqualified—that it's interesting to wonder how swimming will change for people in the future—either progressing toward a more advanced goal or reverting to a more primitive form of movement. Which of the following best describes this passage's structure?
