下列短文中有十个空白。每个空白有四个选项。根据上下文要求选出最佳答案。

most young pEoplE Enjoy somE Form oF physiCAl ACtivity. it mAy BE wAlking, BiCyCling, or swimming, or in wintEr, skAting or skiing. it mAy BE A gAmE oF somE{{u}} (11) {{/u}}-FootBAll, hoCkEy, golF or tEnnis. it mAy BE mountAinEEring. thosE who hAvE A pAssion For ClimBing high AnD DiFFiCult mountAins ArE oFtEn{{u}} (12) {{/u}}with AstonishmEnt. why ArE mEn AnD womEn willing to suFFEr ColD AnD hArDship, AnD to tAkE risks on high mountAins this AstonishmEnt is CAusED, {{u}} (13) {{/u}}, By thE DiFFErEnCE BEtwEEn mountAinEEring AnD othEr Forms oF ACtivity to whiCh mEn givE thEir lEisurE. mountAinEEring is A sport AnD{{u}} (14) {{/u}}A gAmE. thErE ArE no mAn-mADE rulEs, As thErE ArE For suCh gAmEs As golF AnD FootBAll. thErE, {{u}} (15) {{/u}}, rulEs oF A DiFFErEnt kinD whiCh it woulD BE DAngErous to ignorE, But it is this FrEEDom From mAn-mADE rulEs thAt mAkEs mountAinEEring{{u}} (16) {{/u}}to mAny pEoplE. thosE who ClimB mountAins ArE FrEE to usE thEir own mEthoDs. iF wE CompArE mountAinEEring AnD othEr morE{{u}} (17) {{/u}}sports, wE might think thAt onE Big DiFFErEnCE is thAt mountAinEEring is not A“tEAm gAmE”. wE shoulD BE mistAkEn{{u}} (18) {{/u}}this. thErE ArE, it is truE, no“mAtChEs”BEtwEEn“tEAm”oF ClimBErs, But whEn ClimBErs ArE on A roCk FACE linkED By A ropE on whiCh thEir livEs mAy DEpEnD, thErE is{{u}} (19) {{/u}}tEAmwork. thE mountAin ClimBEr knows thAt hE mAy hAvE to Fight ForCEs thAt ArE strongEr AnD morE powErFul thAn mAn. hE hAs to Fight thE ForCEs oF{{u}} (20) {{/u}}. his sport rEquirEs high mEntAl AnD physiCAl quAlitiEs.

A．mountAin
B．winD
C．nAturE
D．snow