4．如图2，点O是△ABC的内切圆的圆心，若∠BAC=80°，则∠BOC=(    )

A．130°                                                    B．100°

C．50°                                                      D．65°

C．                                                    D．

A．                                                   B．

3．若使有意义，则的取值范围是(    )

2．如图1所示，右面水杯的俯视图是(    )

C．                                        D．

A．                                      B．

1．下列运算中，正确的是(    )