认识的客体的属性有（）。
A.客观性
B.对象性
C.社会性
D.历史性
参考答案：A, B, C, D
There no cars or planes many years ago.
[ ]
A. is
B. are
C. was
D. were
如图所示，要使灯L1、L2串联，则应闭合开关______，要使灯L1、L2并联，则应闭合开关______．
