北京奥运火炬成功登上珠峰，如图所示是火炬手从拉萨出发攀登珠峰的线路图，据此图判断下列说法正确的是（ ）
A．由起点到终点火炬手所走线路的总长度等于位移
B．在计算登山运动的速度时可以把火炬手当成质点
C．火炬手的平均速度等于线路总长度与火炬手所用时间的比值
D．火炬手的平均速度等于从拉萨到峰顶的直线距离与火炬手所用时间的比值
A、位移是矢量，大小等于初末位置间的距离．故A错误．
B、在计算登山运动员的速度时，形状和大小可以忽略，可以看成质点．故B正确．
C、平均速度等于位移与时间的比值，不是路程与时间的比值．故C错误，D正确．
故选BD．
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| For 52 years my father got up every morning at 5: 30 a. m., except Sunday, and went to work.I __1__saw my father home from work ill.He had no hobbies, __2__taking care of his family. For 22 years, __3__I left home for college, my father__4__me every Sunday at 9?00 a. m..He was always interested in my__5__, or how my family was doing, and I never once heard him__6__ about his lot (生活状况) in life.The calls even came when he and my mother were in other states. Nine years ago when I__7__my first house, my father,67 years old, spent three days__8__my house.He would not__9__me to pay someone to have it done.All he __10__was a cup of tea, a paint brush and to talk to him.But I was too__11__.I had a law practice to run, and I could not take__12__ to hold the brush, or talk to my father.__13__things happened several times later. The morning on Sunday.January 16,1996, my father telephoned me__14__, this time from my sister's home in Florida.But the__15__came again at 4?40 p. m.that day.My father was in the__16__in Florida with an aneurysm (动脉瘤). I got on an airplane__17__, and on the way, I__18__of all the times I had not taken the time to talk to my father.I determined that when I arrived, I would__19__for the lost time, and have a nice long talk with him. I arrived in Florida at 11:30 p. m., my father had__20__at 9?12 p. m..This ti  me it was he who did not have ti  me to talk, or to wait for me. | ||||
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