题目

已知等差数列{an}的前n项和为Sn，若＝a1 ＋a2011，且A、B、C三点共线(O为该直线外一点)，则S2011= ( ) A．2011                       B. C．22011                       D．2－2011 答案：B -----They used to be good friends, but now they are like strangers. ----- How _____ this ______? 　 A. were; come about 　 B. did; come about 　 C. were; taken place 　 D. were; happened