秦朝当时通行于全国各地的货币是( )
A:刀币
B:五铢钱
C:圆形方孔钱
D:鬼脸钱
在四边形ABCD中,“AB→=2DC→”是“四边形ABCD是梯形”的( )
—Sir, would you mind my sitting next to you?—__________. My father will sit here in a minute.