子帧结构中有三个特殊时隙为（）。
A.SS
B.DwPTS
C.GP
D.UpPTS
参考答案：B, C, D
--- It took me two hours or so to walk here.
--- But you ______ here in Billy’s car.
A．could have come
B．must have come
C．must come
D．could come
掉期交易中，报价者所报的S/B价表示询价者卖出近期，买入远期被报价货币的价格（）
