C．                                                     D．

A．                                                     B．

7．设数列是等差数列，且是数列的前项和，则

C．                                      D．

A．                                         B．

6．若奇函数在区间上是增函数，又=0，则不等式的解集为

A．                         B．                    C．                          D．

5．已知离心率为的曲线，其右焦点与抛物线的焦点重合，则的值为

C．                                                            D．

A．                                                           B．