AboutninemillionpeoplelikerockclimbinginAmerica．Millionsmoretakepartintheactivityaroundtheworld．Somedoitjustforfun．Otherscompete．Climbingtakesstrength，controlandgoodbalance．Climbershavetopullthemselvesstra
About nine million people like rock climbing in America．Millions more take part in the activity around the world．Some do it just for fun．Others compete．
Climbing takes strength，control and good balance．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 onto rocks by only their fingers or toes．
There are several kinds of rock climbing．Traditional rock climbing is done outside．Climbers wear ropes and tie equipment to the rocks as they climb many hundreds of meters up．They also connect their ropes to the equipment．If a climber slips，a rope can stop him from falling．
Sport climbing is similar．However，in it the protective equipment is placed in the rock all the time．There is also indoor climbing．Rock walls made of wood have places for the climber's hands and feet．
Ice climbing is exactly as it sounds．People climb glaciers or frozen waterfalls instead of rocks．They use special equipment for the ice．
And then there is bouldering-climbing rocks （巨石攀岩） between three and seven meters high．It is quicker and stronger climbing．Many climbers like bouldering because they can use less equipment．Climbers often need only special shoes and chalk （防滑粉）．All climbers use chalk to keep their hands dry．
Most rocks have cracks and holes and parts that stick out．Climbers use these for foot-holds and handholds．Climbers use their legs to climb．They try not to pull themselves up with their hands or arms．Arms and hands are for position and balance．
People almost always climb in groups of two or more．Climbing alone is very dangerous．Expert rock climbers say only the very best in the sport should do it．
49．The writer mentions the numbers in Paragraph 1in order to show that___．
A．people do rock climbing just for fun
B．rock climbing is popular around the world
C．people arou