下行通道不通时，以下（）规约还能传递数据。
A、IEC101
B、CDT
C、DISA
D、DNP3.0
参考答案：B, C
Keys should never be hidden around the house since thieves _______ know where to find them.
A．virtually
B．unavoidably
C．reliably
D．invariably
施工现场的昼间噪声应不超过（）dB。
A.55
B.60
C.65
D.70
