题目

Mr. Green stood up in defence of the 16-year-old boy, saying that he was not the one ____. A. blamed                     B. blaming            C. to blame                  D. to be blamed    答案：C已知b>0，直线(b2＋1)x＋ay＋2＝0与直线x－b2y－1＝0互相垂直，则ab的最小值等于(　　)A．1B．2C．2D．2