听力原文：There's no doubt that athletes are playing hard enough to suppress immune defenses. The normal population in Australia expects to get between three and four upper respiratory infections each year. But if you look at groups of elite athletes, about 15 percent of those athletes can have six or seven or more, even up to 11 or 12. They seem to get more vulnerable as they train harder. Elite athletes are likely to get more respiratory infections than Ordinary people.