题目

3.若向量与不共线，a·b≠0，且，则向量与的夹角为（    ）A.0         B.              C.              D. 答案：答案:D解析:∵c=a( ) －b,∴a·c=a·a－ ·ab=0. ∴a与c的夹角为. Sarah :What can you refer to if you want to know how tall the tallest person in the world is?小题1:   is only one place ,where you will find the information. And that ' s the GuinnessBook of World Records. This morning we have someone from the Guinness Company that produced that famous book , Tomas  Manning. 小题2:   to the  program, Tomas !Tomas : Thanks, Sarah. It ' s a pleasure to be here.Sarah : Perhaps you could start by telling us where the idea for the book came from?Tomas : Well ,it was first suggested in the early  1950s. Sir Hugh Beaver .the managing director of Guinness, was out shooting birds with some friends. A bird   小题3: ( fly)  away so  quickly that no one was able to shoot it. Sir Hugh wondered whether this bird was the fastest bird in Europe. And it wasn't the fastest. He wondered   小题4:   it was.Sarah :So I suppose he went to the    小题5:  ( near)  library to look for the information and he couldn't find it.Tomas : Yeah , that ' s  exactly what  happened. And  this  made  Sir Hugh  think  there   小题6: be other people in the same  situation who wanted this kind of information. He thought that ,  like   小题7:  ,people would be interested in finding facts about the records to satisfy their    小题8:  ( curious) .Sarah : So  小题9:  idea for a book of records was born. And when did the first book' come out ?Tomas : A few years later, in  1955. S0   小题10:    ( answer)  your question : the  tallest  person  in the  world is 231. 7cm tall.