—Were you at home at 7 o'clock last night?

—Yes, I _______ dinner with my mother. [ ]

A. was having

B. am having

C. have

D. had

统计抽样样本及非统计抽样样本的重要区别是统计抽样样本( )。

A．不需要判断；任何项目是由公式算出的

B．所需样本数较少

C．可获得较正确的结果

D．控制抽样风险可量化