[单项选择]

Last weekend, sportsmen and women of an unusually hardy disposition descended on Sherborne, a pretty Dorset town. There, they swam twice around Sherborne Castle’s lake, cycled 180km and then ran a marathon. The winners of this gruelling race—Britain’s inaugural Ironman triathlon—were rewarded with a spot in a prestigious race in Hawaii, where yet more pain awaits.
For a sport barely known in Britain five years ago, triathlon has grown at a sprinter’s pace. This year the British Triathlon Association, the governing body, will sanction some 450 triathlons, duathlons (running and biking ) and aquathlons (running and swimming). These vary from tough races aimed at endurance junkies to shorter events designed to lure newcomers. By far the most successful is the London triathlon, which, three weeks ago, brought 8,000—half of them first-timers—to the Royal Victoria Dock in east London. That made it the world’s biggest.

A. the practical reasons for the growth of swimming
B. the echoes of jogging craze of the early 1980s
C. the reasons for the wide television coverage
D. the driving forces behind the development of triathlon