系统故障可分为（）。
A、固定性故障
B、偶然性故障
C、固定性故障、偶然性故障
D、突发性故障
参考答案：C
_____ many times, he finally understood it. [ ]
A. Told
B. Telling
C. Having told
D. Having been told
债务人或者第三人将其动产或权利移交债权人占有，将该动产作为债权的担保是指( )。
A．抵押
B．留置
C．质押
D．留置
