由于光信号很微弱,因此要求光电检测器具有仅可能低的()
A.速率
B.误码
C.噪声
D.漂移
参考答案:C
His uncle went abroad in 2010, and _______since.
A.has not been heard of
B.had not been heard of
C.had not heard of
D.has not heard of
在工件既有平面需要加工,又有孔需要加工时,可以采用()。
A、粗铣平面→钻孔→精铣平面
B、先加工平面,后加工孔
C、先加工孔,后加工面
D、任何一种加工形式