A.充分                                                            B.必要

C.充要                                                            D.既不充分也不必要

A.两个点                                                        B.四个点

C.两条直线                                                     D.四条直线

A.充分不必要条件

B.必要不充分条件

C.充要条件

D.既不充分也不必要条件

①若曲线C上的点的坐标都是方程f(x,y)=0的解，则C的方程是f(x,y)=0  ②若以方程f(x,y)=0的解为坐标的点都是曲线C上的点，则方程f(x,y)=0的曲线是C  ③若以方程f(x,y)=0的解为坐标的点都是曲线C上的点，则曲线C的方程是f(x,y)=0

A.0                                                             B.1     

C.2                                                             D.3

A.x＋y=5                                                          B.x＋y=5(x≥0)

C.x＋y=5(y≥0)                                                 D.x＋y=5(0≤x≤5)

A.一个点                                                        B.一条直线

C.两条直线                                                     D.一个点和一条直线

A.y=x与y=

B.(x－1)²＋(y＋2)²=0与(x－1)(y＋2)=0

C.y=与xy=1

D.y=lgx²与y=2lgx