( )是一种即期易货交易。
A．国债现券交易
B．国债回购交易
C．国债期货交易
D．国债衍生交易
参考答案：A
_____ many times, but he still couldn't understand it.
A．Having been told
B．Though he had been told
C．He had been told
D．Having told
选煤厂水灾防治与应急的措施有（）。
A.确保设备安全可靠
B.组织生产
C.巡回检查
D.召开会议
