单项选择题
A．they have a lot of free time B．they can go to hospital if they are injured C．their lives lack excitement D．they no longer need to hunt for food
A．Dangerous Sports--What and Why B．The Boredom of Modem Life C．Bungee Jumping--Is It Really Dangerous D．The Need for Excitement
A．jump as high as you can B．slide down a rope to the ground C．attach yourself to a rope and fall to the ground D．fall towards the ground without a rope