（）产生的摩擦力最小。
A.干摩擦
B.液体摩擦
C.半干摩擦
D.半液体摩擦
参考答案：B
Hillary Clinton arrived in Beijing yesterday, ________the start of her short visit to China.[ ]
A. marked
B. having marked
C. marking
D. to mark
基差的大小主要受到（）因素的影响。
A.时间差价
B.品质差价
C.心理差价
D.地区差价
