根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
Rock Climbing as Sport and Art
An estimated nine million people rock climb in the United States. Millions more take part in the activity around the world.    Others compete. Rock climbing can be dangerous. But there are many methods and protective devices that can increase a climber’s safety.
    Climbers have to pull themselves straight up the face of very high rocks or walls. So they have to be strong enough to carry their own weight. And climbers sometimes have to hold on to rocks with only their fingers or toes.
There are several kinds of rock climbing. Traditional rock climbing is done outside. Climbers wear ropes and attach devices to the rocks as they climb many hundreds of meters up. They also connect their ropes to the devices.     Sport climbing is similar. However, in those cases the protective devices are permanently placed in the rock. There is also indoor climbing. Rock walls made of wood or concrete have places for the climber’s hands and feet.
  People climb glaciers or frozen waterfalls instead of rocks. They use special equipment for the ice.
And then there is bouldering（巨石攀岩）— climbing rocks between three and seven meters high.     Many climbers like bouldering because they can use less equipment. Climbers often need only special shoes and chalk. All climbers use chalk to keep their hands dry.

A．Ice climbing is exactly as it sounds.

B．Some do it just for personal satisfaction.

C．Some go climbing at weekends or in holidays.

D．It is a quicker and more intense（剧烈的；紧张的）kind of climbing.

E. If a climber slips, a rope can stop him from falling.
F. Climbing takes strength, control and good balance.
G. It is more challenging and dangerous, but also more fun.